bring a lap top,ipod, window seat! talk to the passenger you're with or something PSP, etc.
A lot of people have made pot brownies and eaten them just before they go in the airport. Said it made the flight way more fun or turned 20 hours into 3.
Snakes On a Plane
Join the Mile High Club (renew your membership every half hour).
squirt people with water from behind and pretend it wasn't you
shit your pants
kick a soccer ball up and down the isle
tell people god spoke to you and that the plane is going to crash
Play Bloodhound Gang real loud on a boombox.