Wear a sling bag for quick access to your stuff without having to go into your big bag on the airplane.
You probably don't need the fancy laundry soap packets to wash your clothes in the sink. You can use a little bit of laundry soap bar in a plastic bag, or in a pinch, some hand soap.
Nice sandals (like Bedrock) and zero-drop shoes (like Lems) can pack real flat into your bag and reclaim some space.
Bring a Heroclip, a carabiner which can double as a hook to keep your nice backpack off the bathroom floor.
Little A6 notebooks fit almost anywhere and are a great way to jot down notes during your trip.