Everyone else has covered the basics, pre-flight.

I'd like to strongly suggest taking something to do, something to eat and something to drink. You're going to be on the plane for a while (and if something happens, maybe a LOT longer than you'd think... 9+ hours sitting in view of the terminal, waiting to take off? It happens).

If you don't take something to drink, you'll pretty much get only what they have, when they choose to give it to you. Take stuff to eat too. It's easy to find trail mix, power bars, fruit bars, hard candy, cookies, honey roasted nuts, etc. in nearly any airport store. I load up on at least a couple of different kinds (salty, sweet) for variety. Grab a couple of bottles of water while you're there. Cabin air becomes very dry.

I always take a sub-notebook as a movie player. It's a great way to pass the time on the flight. You can buy small dvd players with builtin screens if you don't have a laptop. And / or take a book or a couple of magazines. An MP3 player with the kind of earplugs that block outside noise are great too. Airplanes are noisy. You do NOT want to be stuck on a plane with nothing to do.

Weird, I guess, but flying sucks the most for me BEFORE takeoff. I find the whole process of getting to the airport, getting through security and getting seated much worse than the actual flight. Once the engines press me back into my seat, I actually start to relax. :-)