The reason you're struggling to think of anything to put on it is because you don't need to be carrying a USB drive.
No aircraft cabin crew have ever put out a call asking if there are any Linux sysadmin onboard with a copy of GParted Live v1.5.0 for 32bit ARM devices .
I have three partitions: First one is Ventoy with a couple of distros per architecture. Partition two is a standard exfat partition for files. Partition three is a small fat16 partition, since there's always that one device someone has (oscilloscope, 3D printer, UEFI/BIOS, etc.) that only supports very simple file systems. I've had to use the fat16 partition more than a couple of times and I don't even work with legacy hardware.
A metal 128 GB USB on my keychain next to the U2F key
16 GB Ventoy partition with:
Clonezilla ('deploying' my system image and backups)
Mint Debian Edition (everything needed to test and recover my Debian systems)
Debian netinstall
Various manuals and reference documents
Portable CrystalDiskInfo and VeraCrypt for Windows
Dumping grounds for files that I intended to transfer between machines, particularly the XP retro gaming rig
An optimistic IF-FOUND.TXT
KeePass
Previously Windows, until once upon a time, I booted into WinRE via Ventoy, got confused between X:, C:, and whatever else, and proceeded to nuke my USB instead of another disk. The Windows installer lived on its own USB happily ever after.
And a LUKS encrypted partition in the remaining space with more documents and a backup of almost all of my photos.
When I last had an everyday carry USB stick (5+ years ago) I found I never actually used it for anything.
I had Ventoy and some practical ISOs, and PortableApps with a bunch of useful software (firefox, foobar2000, GIMP, notepad++...) for when I was using someone else's Windows PC.
...think I stored like two word documents on it, ever.
Mine is mostly lighting console show files of various concerts/comedians/dance performances I have been the lighting designer for. I know my use case is different than most people's, but hey, you asked.
512GB Ventoy, every version windows that can boot from ISO. Gandalf's win 10 PE, gandalf's 111 PE, Debian live ISO, max versions of Debian and NixOS, silver blue and fedora. Ubuntu along with LTS. I could have put my crypto partition on it, but I actually like keeping that as a separate key.
MediCat is Ventoy with a ton of images and a config file.
It seems great, although I chose to roll my own as MediCat had a lot of Windows-centric images i have no need for.
I also have a USB stick on my keys. Mostly I keep books I'm reading, favorite movies, stuff like that. Then when I'm hanging out with friends later and we're talking about what we're watching I have it all ready to share.
My "everyday carry" isn't a USB stick, but it can act as one - and much much more: I always have my trusty Flipper Zero with me, and the image I carry in the mass storage emulator is the Linux Mint installer, with extra space in the image to store small files.
To be honest, the Flipper Zero's mass storage emulator turns it into the slowest USB stick you never saw. But in a pinch, it's there and it's usable. I use my Flipper for a variety of other things all the time - including, with my laptop, as a presentation remote and secondary mouse - and I almost never need a USB flash drive. So slow though it is, it's enough for when I do need one.
Mine is a durable, metal 128GB stick. It lives on my keyring and has a relatively recent copy of Arch on it. It's handy for fixing broken laptops and rescuing data. A friend has a more advanced one, with multiple distros on it for different diagnosis options.
I got two identical 64gb sticks. One's for a Ventoy setup with a bunch of different ISOs, in case anything has to be done and/or recovered. The other just has occasional random files i might need
64 GiB, two partitions, one with my files including Keepass database, the other with Ventoy with ISOs for Linux Mint 21.3 Cinnamon, Debian 13.5 KDE, NixOS Gnome, Win 10 and bazzite
I used to leave some usb device with multiple bootable isos lying round my table, but I found out that every time I needed something, none of them would serve me, and I had to download something else, so I don't do that anymore and just download and write isos as I need them. Oh, but I still keep an old 4gb usb stick with some random distro on it, just in case my pc becomes unbootable and I have to do some maintenance/data rescue.
Before Google Drive and Syncthing I relied on such a USB device. Today, no matter what I put on the stick, it's outdated or entirely not what I need when I need something.
Having any stick on hand, and being able to flash an image from your phone, that's nice
I don't really carry one anymore, but the one I have at my desk has Ventoy and LMDE on it for when I need to mess with something requiring my system to be down or modify my OS partition. I don't really do much on other PCs except when I have to help my wife with something.
When I was working at my last job I carried 2-3 with a ton of database backups and proprietary software and firmware files for clients' automation systems. Kinda don't miss it at all, but it sure made me feel important, lol.
Well if you don't have an actual use case for it, don't try to artificially find one.
The only thing I use USB sticks for nowadays is for OS installs.
For everything else their write speeds are slow (even the more expensive USB sticks slow down to a crawl after what feels like not even one complete overwrite) and they are unreliable.
Sure, if you want to carry around random OS installers and live environments, go for it. I personally don't have a use case for it.
right now mine has manjaro+cinnamon. i booted my wife's Win11 laptop to it so she could test drive it and within ten minutes she was asking how to get to the installer. i hope to repeat this process with others as well.
I have a Debian 12 install on a 5GB partition (btrfs compression is magic), and the rest is exfat. It has rEFInd as the bootloader, should be pretty good at detecting and running other OSes with bootloader problems.
I have a copy of MX Linux installed, as well as encrypted copies of all my most important data and a few commonly used portable utilities for windows and Linux. It's mostly just an emergency backup, but I have used the other parts before, just very rarely.
Yeah main thing is Ventoy and images for windows 10 and 11. I also have some basic tools, and some portable versions of some games I like (OoT, Warcraft 3, etc).
The only solid reason I can think carry anything on a USB stick is if you're going to be in an area without Internet. If you're in an IT role where you're interacting with end-user machines all the time, then the answer would obviously be some sort of live environment to troubleshoot or fix issues. In that case, load a Ventoy partition with a few different images, and and be done with it I guess.
If you're thinking like a Prepper or whatever, keep a copy of Wikipedia, and some survival books maybe? Maps? That's all I can think of. If you're going this far, better carry a backpack with portable solar panels, a large battery, and a lifejacket. None of this matters when you don't have food and water though, so...