I agree about taking the car seat for a 2 1/2 year old. We have three kids and all of them have had frequent flier accounts since they were babies (we live in the boonies). The familiarity and security of their own car seat really seems to help- but not all will fit, so be sure you take a narrow, booster-type seat.
Another hint is that you can check the stroller if you have a sturdy rolling bag with you on the plane. This is very handy. Just extend the handle on the rolling bag, sit the child on the top of the bag while it's slightly inclined, and go! Our kids thought this was the best! Of course, if your child is squirmy, it doesn't work. We made some pretty tight connections and attracted some smiles using that technique.
The biggest thing is- act like it's a very interesting and exciting car ride. If they get even the
slightest hint that you're nervous about flying, they'll pick up on it and respond fearfully. Our babysitter sat next to my (previously) unafraid daughter one time and repeated to her over & over "There's nothing to worry about." It tooks us years to undo that mistake! The most I would do is drive by the airport one day and casually say that you'll all be taking one of those big planes to Florida, won't that be cool? When the engines rev, I get out a book and read. The kids figure out it's no big deal and they're not afraid.
Also, planes can be hot one minute and cold the next. I dress the kids in layers (sweater, short-sleeved shirt, pants) that can easily be removed, and no sandals because their feet will freeze. We love zip-off pants for this reason. Sometimes they wear Teva sandals with socks- though that's not high fashion it gets me out of having to pack tennis shoes.
Also, bring TSA-approved snacks & water. You won't get enough of either on the plane or while waiting in those interminable lines. Little magnadoodles, books and an occasional surprise trinket are really great helps. I'm not a gum fan, but that is great for popping ears and so is any chewy food- tootsee rolls or milk duds are our favorites!
It goes without saying that the favorite blankie or toy HAS to come! You can forget anything else, but don't forget that
