Hi T.,
My advice may be a bit different from the others, but my son is 2.5 (3 at Thanksgiving) and he's flown on about 10 trips now (my hubby works for SWA). We have always taken his carseat with us, but we use a gogoKidz travelmate cart and it stays attached to his carseat always (even strapped into the car, though they say not to do that- don't know why). Here's the url for the cart...http://www.gogobabyz.com/products/gogo_kids.html. We always take it because we always need it wherever we're traveling to- the cart makes the carseat double as a stroller, so it works out great. (If you get one, just don't forget to ask for a "seatbelt extender" when you get on the plane- can't really attach it w/out). One other reason we've always used the seat is so he knows that he has to stay seated and strapped in at all times (just like in the car). We've never let him out of the seat on the plane, unless we just had to change the diaper because it was so full, but then he's right back in it- straps and all. He's come to know that that's the way it is on the plane- everyone stays seated- so he doesn't fuss about it because that's all he knows. There's no where for them to go, so why let him out? If we have a layover I let him out to run then (always have his monkey harness, with the tail leash for running in the airport, so he doesn't get hurt- you can get those at Wal-Mart).
We always bring him a juice cup and a milk cup- they sometimes ask what's in his cup when we go through security and we tell him it's juice- they're happy with that explanation (it's a 10 oz cup, by the way). We've never had them tell us to throw it away and we've gone through several different airports- San Fran, Dallas (both) Philadelphia, Albuquerque, etc). We also take the milk boxes as extra (he drinks a lot of milk, esp. when it's a long travel day). They're like juice boxes, but they're milk (Horizon and Organic Valley make 'em).
We always take his portable DVD player and he usually watches movies if he's not sleeping. It cost less than $70 at Best Buy or somewhere like that. I like the headphones that slip around the back of the ear for him best. (It's too loud on the plane not to have headphones because if you turn it up all the way it bothers everyone around you- I've had flight attendants tell me to turn it down, but then he can't hear it). I take this because he really doesn't have space to play with stuff, so he doesn't. He's usually very on the go or has lots of toys and there's never room in his bag for lots of toys.
I also usually give him some antihistamine (or Benadryl) before we get on the flight. Some people say it's bad to give them this to make them sleepy, but seriously, how often is it done and why not? He often sleeps for hours on the flight and we're both much happier that way. I take Dramamine to make me comfortable and sleepy, why not something to help calm them down? I think it's kinda cruel to put a child who's normally very active strapped in a plane for hours without helping them get some sleep. Don't try Dramamine for him, though, whatever you do. For some reason, at this age, and I don't know if it's that I can't get the dosing right or what, but it just makes him real cranky and does not put him to sleep. Won't be doing that again!
Also, if he does have a problem with his ears on the first flight, some advice I got was to give them a decongestant at least an hour before landing (if you can give it to him when you get on, if the flight is less than four hours because that's when it wears off). This makes their ears fine- no pain or popping. I've tried everything- drinking, eating, chewing gum- on the way down, but if his ears are hurting him he won't do any of it! Ahhhh! Plus, he just swallows the gum.
Just remember to try your best to stay calm, because, I'm sure you already know, but if you get worried, frantic (if he's crying or something), half of his reaction will be because of yours. Kids react to what their parents are feeling, so the calmer you can be (maybe take some Dramamine yourself? (though it can make me cranky, even though I'm calm) the better.
This probably sounds bad too, but if my child screamed on the flight, I would simply cover his mouth with my hand- it actually makes them stop quicker. If he's crying, I let him cry, but mine tends to scream when very mad or cranky or whatever and I feel so bad for the people around us when he does that. He's gotten much, much better about not screaming since I started the covering the mouth thing. He doesn't like it, so he stops.
Sorry this was so long, but you asked, and we have a lot of experience. Going to Cali at the end of the month and I'm not nearly as apprehensive about flying with him as I used to be, now that we've gotten the kinks out.
Hope this helps- let us all know how it went!
A.