P.F.
Hi A.!
I have both travelled with a toddler and have a girlfriend that takes all 4 of her kids to Scotland every other year. So here's what works for us.
My daughter is now 3 and since she was 2 I stopped trying to make her sit in the car seat on the plane. She hates it.
As for things to do, my girlfriend fills her kids backpacks with new stuff for each trip. For example, she fills it with new crayons/markers and new coloring books. Perhaps a new book to read to them or do activities in. Small canisters of playdough (which can be tons of fun and not noisy at all!)
A few small snacks. A new Barbie/doll etc... At this age, the fact that there are new things is enough to keep them interested and before you know it you're there.
I have also given my daughter Benedryl before a trip and not only did it help but she took a nice little nap. It helped to get her thru the take off.
Lastly, I always take a copy of my daughters birth certificate but have yet to be asked for it. We have been on 7 trips with all different airlines.
Good luck!
P.