E.P.
Deck of cards or various card games, small dvd player or laptop to watch a movie, coloring books or activity books / word search for older child. Gum for chewing to pop ears. Don't know about that clay idea - wouldn't want to bring anything on a plane that could cause a mess and, eventual headache. I've travelled a lot with my kids and have never considered bringing it. My son always packs a few hot wheel cars and I pack a couple new items that the kids didn't expect to receive (i.e. coloring books or small toys) is always exciting. Be careful of anything that would be too noisy or beeping or something that will make them fidget in their chairs too much....so that you don't distract other passengers. Keep it easy so that you have fun and aren't exhausted! That's why that dvd is a good idea - one set of headphones w/ two children keeps them attached! Have fun!