Carrying your own pen might help you as you might have to fill some custom form if you’re visiting another country.
It is dangerous to sleep with an unfastened belt as you never know when the airplane might hit turbulence or an emergency landing.
Though all the flights are cleaned before boarding but still it is not as clean as it should be. It is advised not to go barefoot in the flight as it isn’t sanitary.
When flying, it will be cold in the airplane, and you might want to carry some warm clothes which are also comfortable.
Having too much caffeine on the airplane might make you restless, instead drink water and fruit juice to let the air circulate and keep you hydrated.
While using the washroom, remember that you’re sharing it with many other people. So, make sure that you close the washroom and maintain hygiene after doing your business.
If due to some dietary issues you have to bring your own food, you can ask the flight attendant to warm up your food whether it’s yours or provided by the staff.