Refillable water bottle
Travel size bottles filled with moisturiser & sunscreen that can be used on face and body
Scarf - because planes can get so cold
Pen - seriously the amount of times I wished I had a pen on me!
Cosmetic case with your makeup & toiletries
Socks - compression socks are ideal
Sleep mask so you can block out the light when having a nap!
Change of clothes - usually something not too bulky like a dress
Jacket - I would normally wear this on the plane but its a good reminder to have one with you
Spare change of underwear!
Sanitiser, disinfectant wipes & mask
And obviously things like your mobile, ID, bank cards - which can all fit in your travel wallet/bag
Hopefully this helps you on your next trip!