The necessities are pretty straight forward and therefore don't need any more explanation: passport, boarding ticket, wallet, phone, and medicines.
As for comfort, I like to wear thick warm socks. I guess real flight socks would be a better option in order to avoid embolism, but I just wave my legs once in a while. Another must is a big scarf. You can nicely wrap it around yourself or use it as a light blanket. Having long hair and glasses, it's great to be able to put your hair up and place your glasses in a safe place if you want to rest. That's why a case for eyeglasses and a hairband always travel along with me.
If you've got a long flight ahead, it's essential to bring something entertaining to keep you busy. I usually have a good book, a magazine, some school books and music with me. Since I'll be away from school for one week, teachers have piled on homework. A lot. At least I have something important to do... But this time, I'll also have my laptop with me because I'm really in the mood for playing a little bit of Sims 3, haha.
Regarding cosmetics, I prefer bringing a couple of moisturizing products because my skin dries properly in the aeroplane. I also like to carry small makeup items like a concealer and an eyebrow pencil, so that I would look a bit fresher after the flight.
So that was a quick list of things I'll be taking with me!
What do you guys usually do during a flight? :)