Our daughter's 4 now, but she's flown at every age. She's a skinny little thing and there was no way at age 2 the regular belt would have done her any good. Her car seat was comfortable for her to fall asleep in, it had side pockets for storing more of her crayons and things, it lifted her to be able to reach the tray better, and we had to bring it with us anyway for the car so it wasn't like it was an added inconvenience.
I know there was a story in the news a couple of weeks ago with a bunch of people injured from severe turbulence, but as someone else said, those stories are rare, so go with whatever you are comfortable with. I tend to err on the side of caution instances like this- bringing the seat was never a big deal, so :shrug: I figured why not. But her car seat said right on there that it was FAA approved and we didn't have to think about buying a new one.
I agree with Katnthemouse about the bathrooms :ROFLOL:
Portable dvd player is your friend, plus I'd recommend some new books your child hasn't seen yet, crayons, snacks, anything that can be played with in a tiiiiny little area. Ours always liked little toy figures she could build stories with. Anything to help the time pass! Have fun!