First things first, you'll need to bring the obvious stuff: your ticket, passport, and any visas required for your destination. Don't forget to check the weather forecast for your destination and pack accordingly – you don't want to be caught in a snowstorm without a coat! And, of course, bring a phone charger, because a dead phone is basically a tragedy.
In addition to the essentials, you'll also want to bring some entertainment for the flight. Books, music, and games are all great options to pass the time. Just be sure to bring a portable charger for your devices, because you never know when you'll need a little extra juice.