Noise canceling headphones. I swear by the Bose Quiet Comfort series. Personally I still have the 25 model (with a third party Bluetooth dongle), that way when the battery dies I can simply swap it out, takes simple AAA ones.
Else I'd recommend to bring slippers to wear during the flight. Feet tend to swell up a bit, so wearing shoes is uncomfortable, and walking in socks as many people do is not exactly hygienic, especially in the bathroom (seriously, who does that???).
I'm also freezing easily, so I'll bring a thin scarf to protect my neck from the long exposure to low temperatures.
Lastly, have a set of fresh underwear, t-shirt and wet towels in your hand luggage, along with a toothbrush & paste and deodorant (make sure the volume is hand luggage capable). Then about 1.5h before landing, lock yourself in a bathroom (ideally the ones in the middle, they are a bit more spacious), strip naked, give yourself a through wash, change of clothes etc., and land arrive somewhat refreshed.
Noise-canceling headphones. Eye mask (some planes might provide one, but get a nice one that fits you). A good mask (planes can be very low-humidity so even if you aren't worried about anything else, this can help keep you more comfortable).
Wear loose-fitting clothing (except compression socks if that's something you want to do) or otherwise comfy clothing.
Other than that, get up and stretch every couple of hours if you can and are not sleeping.
I have flown from NY to Tokyo multiple times (which is like 15 hours depending upon weather).
Elastomeric respirator like 3M 6200. It will be more comfortable than an N95 if worn for a long time. But wear an N95 (maybe change them every few hours as they get damp) if you have to. Plane rides are super spreaders and so are airports.
I picked up a set of AR glasses for my last flight and was surprised how much of a game changer they were. I plugged them into an older Samsung phone and the Samsung Dex software let me switch the main phone screen off. This gave me something like 9 hours of video time on a larger screen that I could watch in any head position, with shows I brought myself.
Screenshot your QR code to board. Crop it to just the code so your boarding zone is missing, and board in the middle of the second main group (Zone 2, Group 2, Etc. Not any of the special categories). No one will stop you.
Pick a seat in the back of the plane. You will deplane slower, but no one fucking cares unless you have a connection
Because of 1), you will board and head straight to the back, giving you time to sort your carry on and backpack/purse.
Stow the carry on immediately, drop your bag into your aisle seat. Remove your seating essentials once you size up your seat.
Bring a magnetic phone mount you can clip to the closed tray table (check amazon for one you like), plug in your charger brick, but not the cable, other passengers will kick it.
Open the overhead air vent nozzles to full, point them at your seat. If you sit, and it's too much, point 1 or 2 of the others away. If you like all 3... Hope the other passengers never notice.
On a long haul you will probably be given a little pillow and blanket. Temporarily toss these in the overhead ontop of your bag. If need a neck pillow, get that out of your backpack. For lumbar support, if you think the provded pillow is enough, grab it after takeoff. You don't want the blanket or pillow now.
Stow your water bottle (bring a refillable 24oz or 36oz tall steel bottle). This will hold the flap of your seat back pocket open a bit. Stow any snacks you want, and gadgets. Overload this pocket, items you consume will decrease over time, so anything goes here, stuff it.
Once you have everything out and stowed, your gadgets, headphones (I recommend over-ear noise canceling if you fly frequently) your phone mount your everything, then stow your backpack in the overhead. Again, no one will stop you. The flight attendants are helping load the plane and prep, and people do this anyways. On a long-haul it's first come first serve, hence the seat selection toward the back.
Raise all the arms of the seats on your asile. This will let the other passengers get in faster. Raise the aisle armrest by pushing the button in the back of the arm by the hinge.
Wait, and fully extend your seat belt while you wait, so it's super easy to grab and buckle later. Wipe down anything you like with a wet wipe, especially your headrest and armrest handles. Keep the armrests up though.
Once your seat mates have shown up, lower the two arm rests closest to you, and plug in your charger cable to the charger brick. Buckle up loosely.
After takeoff, use the rest room immediately, grab your blanket if you want to rest, and settle in. Late notice, but if you wear slip ons: slip them off now and relax in your seat. You can change socks after landing. Your feet will thank you. At this point, raise the headrest if you need to, and bend the sides, most headredts are now adjustable on the sides as well and can form a C shape to support your head. This is not as good as a neck pillow bit helps tons when combined with one.
During flight, press the hinge button on your asile armrest again whenever you need to get up, to make getting out easy. If anyone needs out, grab your phone, and unplug your cable from the charger brick, and sidestep into the aisle, take two steps forward or back, away from the nearest restroom, and then reseat but don't lower the armrest until they return. DO buckle again. (Freak turbulence on long hauls is no joke sometimes).
Bonus 1) Lookup and purchase a plastic shim for AC adapter prongs online. Maybe 5 bucks, infinitely reusable. US airplane plugs tend to be very very loose due to extreme overuse. This will keep you from chasing your charging brick around the floorboards.
Bonus 2) For headphones, Bose Quiet Comfort or Sony WH1000XM3 or XM4s. The XM3 and XM4s IMO are superior noise cancelling to the Bose (subjective), and both fold up and are more compact than the later Sony XM5 series. You can find either of these "renewed" on Amazon sometimes for a huge discount. Buy them and never look back.
This works on 99% of flights. You get to stretch out as much as your seating allows, should have all your stuff accessible, and be comfortable to rest if you can. Personally I am too tall to sleep comfortably on most flights so instead I listen to podcasts or read something with very low volume background orchestral music as background to avoid silence/white noise. You'll have to adjust for what works for you, but that early start gives you tons of time to get situated and I think this makes the real difference.
Lots of good advice in this thread already, but I want to add a few details:
that loose hoodie would be even better if the pockets zip up. Losing important items on a plane sucks. Also the pockets work great as a security checkpoint stash: remove your metal and empty your pants pockets all into your sweatshirt pockets, zip them, remove and put in the bin. On the other side you put it back on and have everything easily available.
if you can't find a zippable hoodie, go with a non-hoodie with zip pockets and a beanie that you can pull down over your eyes.
for sleep aids, it's a good idea to wait until after the first meal, which is usually within the first two hours of the flight, but you can ask and make sure.
Most long haul flight have seats with decent head rests but for shorter flights I want to sleep on, I use a soft cervical collar. More comfortable without it on but it means you don’t wake up with your head in a weird position and sore neck.
3D eye masks mean your eye lashes aren’t brushing against the eye mask.
I prefer in ear headphones as it means you can rest your head against the window or whatever, it is more comfortable and you don’t get buzzing from the plane being carried through.
I got a great travel hoodie that has heaps of pockets, some on the inside, a big hood with a fold down flap for extra darkness, ensures a comfortable temperature etc.
For shorter trips I’d recommend a moisture wicking long sleeve top to help keep you at a comfortable temperature but not take up space in your bag.
Edit: The hoodie I got years ago and still have was a Burton Sleeper Hoodie, sadly it seems they have stopped making them?
As a frequent flier I'd say the most important thing is what you do before and after your flight, not during.
Go in well hydrated (get those electrolytes!) and well rested. If you're flying far east/west, adjust your eating and sleeping ahead of going, to make sure the adjustment is not so hard on arrival. If you're arriving in the morning, try to sleep on the plane... if you're arriving in the evening, don't sleep on the plane. Additionally, when you arrive, wait until the appropriate time to sleep/eat as not to prolong jet lag.
This depends entirely on your seat. If you're flying economy, a travel pillow and a large loose hoodie helps you sleep in a position that doesn't fuck you up too much.
Bluetooth ear buds are are really nice to have. I'm tempted to say that noise cancelling isn't that useful on a plane, as there will be plenty of brown and white noise.
Depending in how long your flight is, consider bringing a portable charging method. Also, most seats on long haul flights have an USB outlet, just keep in kind that these are pretty low wattage and won't allow you to charge very fast.
But by far the biggest comfort you can buy is a seat upgrade. Something as simple as extra leg room is worth it. But if you can defend the price tag, business class is the only way to fly really comfortably.
Earplugs are number one. I also suggest compression socks since no one else has, they help with restless legs since you sit there for so many hours. If you have the money, a steam deck :)
Going alone? On a wide body if the middle has 4 or 5 seats, move to an inside aisle seat next to a couple or group of three, respectively. They're more likely to disturb each other to get up for bathroom breaks than you. If you can do this with one seat between, that seat will be one of the last to fill.
I love me some window seats, but on the long haul it sucks to have to wake peeps to go take a piss.
Do get up and walk the plane. Your legs will thank you.
Buy a little sign that sticks on your seat to let the flight attendants know to wake you for food or do not disturb.
Take a thin, snug hoodie. When your ready to sleep, take your arms out of the sleeves, zip it up, and cross your arms across your body. You'll sleep better and your back and shoulders won't feel as strained. I also have a long, wide scarf that i use for this. For neck pillows, i like the turtl one -hard but kind of flexible plastic with a wrap around sleeve. it works well and it's easy to pack.
Some good suggestions here already. Adding one more - bring water onto the plane. Stay hydrated. As a bonus, it gives you an excuse to go for frequent walks to the bathroom.
Before you get on your flight, get a bottle of water and chug it as fast as you comfortably can. Have another one to drink throughout the flight. This keeps swelling of your hands and feet down. You'll have to get up and pee a lot, which is why an isle seat is a good idea, but you'll be so much more comfortable during and after the flight.
Tbh, an edible if you are into that and comfortable with it. Definitely bring some headphones and download some audiobooks, music, or podcasts you like. A sleep mask if helpful if those are comfortable for you and other people seem to like those neck pillows.
Ear plugs - not just noise cancelling headphones. It's much easier to sleep with ear plugs than with headphones. And headphones can get uncomfortable after many hours. And if you want extra quietness you can use both the earplugs and headphones at the same time
wear clothes that don't melt in a fire (no polyester)
Facemask
Earplugs
Antidiarrheal pills
Wrist strap for your phone (so you can hang it on the seat in front of you and watch your shows)
My advice, travel light, the minimum you need, sure you might be on the plane for 20+ hours, but once you arrive where your going you have to lug all your extra stuff.
Crocs or sandals. Wear them with socks. This keeps your feet dry so they don't smell and you can easily remove them for comfort and put them back on to go to the bathroom.
And
Any noise cancelling headphones with something to play music or podcasts. Even if you sleep through it, planes are loud, you should protect your hearing.
Any kind of headphones that block out some noise. Even if they aren't noise cancelling, if they reduce the sound coming in just by physically being there, it's nice.
A hoodie with a massive hood, if you like hoodies.
I prefer sandals and socks, so I can take them off quickly. But that depends on your luggage situation.
When I flew intl I asked a doc to give me a prescription for two zanax (one each way) to be super chilled out and ended up asleep most of the way. Not sure if that's common, but I think it might be worth asking. Note: had we had an emergency landing, I would not have been able to protect myself, but that's because I mixed it with a bit of alcohol (which you should not do).
Silicone water bottles take up no space and travel well. Extra leg room seats in normal economy are usually narrower than normal seats due to the table and entertainment. Also no unseat storage, but it's less of a concern because once the flight is in air can just get your bag down.
I'm 190cm tall and 150kg. I just survived an 11hr flight on Turkish air boeing 777, following an 6hr flight on a Airbus a330 in economy on both. The Airbus was more comfortable. But Dramamine is your friend.
Sealed bag of cookies/chocolates/whatever as long as there are a decent number. Give it to whichever flight attendant is closest to your seat when you board. Most crews will have your back for the whole flight after that.