I have to second Deb on the Magna Doodle. We got a travel-sized one and Ryan LOVED it! (It's now in his church/quiet toys bag and usually gets us about 4-7 quiet minutes there ). Cars, stuffed animals, books, and (my old stand-by) your cell phone will help, too. I think we are going to have to invest in the portable DVD for our next trip. I'd imagine it would be useful in a long car trip, too.
My best advice: I hope you bought a seat for you lo (instead of being a lap child), b/c I've found that can make all the difference if you want him/her to sleep. It will be worth any money you have to spend, trust me!!! If not, I'd recommend gate checking your car seat instead of checking it, b/c if there is an open seat, you can grab it and use the carseat. (This works for the US's Southwest airlines, anyway).
Don't worry about you lo eating too much. Keep that food and milk coming. Erin gave a good list of munchies. Gerber also makes freeze dried apples, corn, and bananas and strawberries. This is real fruit with no added sugar, so it's a good way to sneak in some "real" fruits and veggies without being messy AND they take a long time to pick up and eat, which is a real bonus.