At this age, I'd recommend
- post it note and/or tape for them to stick to things at will or try to unstick from their fingers and clothes
- something to gum on that they've never seen before
- fun fabrics and textures they're not used to
I learned this tip on here, but make sure you don't bring out all your distraction and entertainment ammo at once. I pack a diaper bag and take out one distraction at a time. Then we take a stroll around the plane, have something to eat, or take a nap. Only one activity out at a time.