Baby/Toddler: Diapers, lots of wipes (for the blowout that will happen either right before or right after you must fasten your seatbelt), hand sanitizer, baby food/snacks, formula if needed, socks, sippy cup, pacifier, 2 changes of clothes, blanket or lovey, carseat (for a place to strap them in if nothing else)
Elementary Children: Video games, headphones (invest in ones that fit or you’ll spend your whole trip readjusting), extra batteries, paper, markers, cards, sweatshirt, socks, extra clothes, blanket or stuffed animal
Mom/dad: book or magazine (but don’t expect to have any time to read it), toothbrush and toothpaste, sweater, ipod and headphones
We love love love the Trunki suitcases we have for our two boys. It’s a hard sided suitcase on 4 wheels that doubles as a ride on toy. I have no affiliation with them whatsoever, but I cannot tell you how wonderful they have been for us. They have been to the other side of the world and back, have held up beautifully, and have provided hours of entertainment when waiting at airports, for taxis, etc. And they hold like 5 gallons worth of stuff – check them out!