I despise flying... I fly so often, and my company always sticks me in the cheapest flight possible... I am 6'4" tall and 180lbs... The seats are so freaking uncomfortable for me that on a flight from Vegas to Detroit I could not sleep at all because I was SO uncomfortable!
As for what to do, see if you can find a Gameboy SP and a bunch of games... In particular grab a fast game and a long game... Something like Wario Ware, which has a bunch of really fun short games you can play in a hurry... Then find something more long and involving like Final Fantasy Tactics or if you like Pokemon at all, I think that is really long and involving.
I do not have a GBSP, so I don't know how long the batterys last, but I think they are rechargeable, so you can not bring extras right? That could be a bummer... Maybe they make something so you can use extra batteries?
And I always recommend sleeping if possible during a flight, nothing will make an eight hour flight go faster then being asleep for seven of the eight