My DS was 16 months old for his first flight last month, and he'll be 20 months for our Disney trip.
The travel sized
Magna Doodle was a hit for us. (He likes magnets on the fridge - so I brought some neat shaped magnets along - they work on the Magna Doodle and can also be stuck to a small metal box.)
So was the
Felt Board I made for him (used the stiff "Easy Felt" for the board - set in a thin box, and cut out felt shapes to stick on it - let me know if you want more details)
The Crayola Wonder markers didn't go over for him, but he was probably just too young yet.
Finger puppets, and other small (especially new) toys were good. I also got books about planes from the library (and store) to read before we went (took one along).
Lots of
snacks were good - and
drinks in a non-spill cup. (DH accidentally packed all DS's snacks in the checked bags coming home! I almost freaked out!

But it was fine, we got some crummy animal crackers at the airport and he ate some of the chewy granola bar the airline brought - plus he slept a good deal.)
He also liked standing on our laps and playing
"peek-a-boo" with people in the rows behind and beside us. (We did have his car seat, but he's not used to being in it for more than 40 min or so, and he got antsy and wanted out after a while.)
Our pediatrician suggested
ibuprofen prior to the flight, to help prevent ear problems. Check with your doctor.
And I read it was a good idea for everyone to use a
saline nose spray before the flight - helps prevent catching germs.
Hope some of these ideas are helpful! I got lots of great ideas on these and other online boards before we went. Have a great trip !
