Hi,
First off, let me say (like a couple of other people have said) flying can be a really nice bonding time with your kids, an exciting and fun adventure together. I think communicating the excitement and fun can be key to making it a great trip.
We flew so much with our first child that we had it down to a science for him--but every kid IS different of course, so here are some ideas that we tried recently with all three kids. (ages 7, 4 and 2)
Gift bags with "surprises"! Little cheapy shiny gift bags from the dollar store work well, or paper or ziplock bags tied with colorful ribbon. Of course depending on the amount of carry-ons he wants to have you might want to minimize the size/complicated-ness of the bag situation.
The surprises can be anything she hasn't seen or played with in a while, or even small toys from the dollar store, crayons and paper with stickers, a few small books and magazines, or the snacks you have already. My newest addition to this idea was small amounts of playdough. It wasn't messy since I was playing with them, and the amount was so small that they didn't want to lose any! It was a good change of pace and a nice tactile outlet.
I also really like to pack things like a small "family" of dolls/characters. You know the hand-holdable size of character type toys. So we had a bag of superheros (they can fly around your seats without the kids having to run), a bag of winnie the pooh friends, a bag of cars, a bag of bendy guys, you get the idea.
Each one can be opened when she seems to get tired with with the last, interspersed with snacks and an occasional walk up and down the aisle (when the seatbelt sign is off, of course!), made the time pass pretty quickly.
Oh, and never underestimate the excitement of take off and landing time, (keeping a drink or pacifier available at those moments is key is her ears are bothering her) as well as the seat pocket, airplane magazine, barf bag--it's an adventure for any doll family to discover a fun cave with pictures and places to crawl in and out of.
By the way, a good thing to think about is when to change diapers. Depending on the airline he's flying, there may be no changing table in the bathroom on the plane. If possible change right before you board. But if she has a blowout stinking diaper on the plane, a great(and small) resource is a couple of safety pins pinned inside your bag and a small airplane blanket. You can pin it to hang from the seat in front of you to the back of your seat and create a little privacy for the fun "laptop change".
I once had to change a two month old on my lap who had an all out crazy up the back with all the clothes full of it kind of poopy diaper on my lap! I had to fully unclothe her. The guys *across* the aisle actually asked me why I couldn't find a more "suitable place for that activity". I was alone with the baby and a feverish 3 year old. Needless to say, that was BAD trip. It was after that trip that I heard the tip about the safety pins.
Hey, I've also had really fun fantastic trips that we've all enjoyed very much. And lots of people are often very helpful and kind on the plane! My advice would be to choose one or two strategies that seem like they'd work for her and keep it relatively simple (ha, I say that at the end of this super long post!).
Hope he has a great time. Lots of times my kids just fell asleep, and that works out great, too. Let us know how it goes!
S.