I let the kids each take a small backpack and leave my bag no more than 1/2 full, as their stuff will migrate there anyway. I have great fun stocking the kids' backpacks w/new stuff for the plane -- stuff like puzzles, a book, magnetic playsets, color wonder sets -- but not too much or they will pull everything out and be too overwhelmed to do anything with it! We load up our mp3/video players w/books on cd, music and new shows to watch. Throw in a bathing suit if you are using ME and want to swim when you get to the resort, or pjs if you are coming in late afternoon.
Definately make sure you have some good/filling snacks! I bring an empty sippy cup and get juice after security. I also like to bring a variety of snacks, especially if we will be flying around a meal time. I bring gum and fruit chews for ear popping and also have them yawn during take off/landing. I also carry childrens tylenol in case of earaches.
Be prepared for security -- it is easier if all of you wear shoes that slip off and on and wear socks so you aren't barefoot on the airport floor. Your stroller will have to be folded to go through the xray machine, so plan your bag and child juggling accordingly!! We are a family of 5 w/2 strollers, so I always feel bad for whomever is behind us....usually they make a beeline for another line!!