I have twins and have flown with them at 23 months, 2 1/2 and 3. THe longest flight was to Phoenix where our portable DVD player did not charge properly and we only had one window seat so that made my kids have a fit right away and the plane ride was horrible.
On all our trips to WDW we have had no issues except for when it is time to turn the DVD player off and the movie is not over.
Aquadoodle makes these great little pages with Thomas, Elmo or Princesses that you can buy. They are compact and come with a pen. Make sure you have water to put in the pen but this kept my girls busy for awhile.
New stuff is key. Even if it is little dollar store toys if it is new it will hold attention for longer than if it is an old toy.
Like others suggested stickers are awesome!!! Coloring books or just lift the flap books too.
Suckers or little candy. I used the suckers for landing when their ears were popping. It seemed to really help with their ears.
I would call the airline and make sure you have all your seats assigned and see if there is anyway you can get the front row behind first class. There is a bit more leg room and they cannot kick the seats in front of them. Unfortunatly AirTran will not let us reserve them but we can ask when we get there.
My daughter picked her nose on one flight and it was bleeding like crazy, so a change of clothes is definatly a good idea.
Things to pack in your baby besides regular items would be.... band aides & kleenex.
They make an item called Lil Toppers (here is a simliar item
http://www.snacktrap.com/Detail.bok?no=32) They are toppers for a water bottle that does not let the water just pour out.
www.snacktrap.com is also great to keep snacks from spilling everywhere. These are also great for inside the park.
Security for us was the hardest to get through cause my kids just did not want to take off their shoes or give up their items to the security people. Once we got through there it was pretty easy.
Most importantly just relax and have a great trip