I have a couple of small Rubbermaid containers that come on each trip. J has a medium-sized one that houses craft supplies: paper, markers, pens, notebooks, pipecleaners (yes, a great in-the-car craft item), popsicle sticks, tape, scissors, etc. It’s amazing the creations that have come out of the backseat with the supplies in this box.
B’s small container is full of games: cards, hand-held electronic games, travel-size versions of popular board games, etc. He also finds new free apps for the ipod touch before we leave on a trip.
Besides these two boxes and a portable DVD player, I don’t pack anything for the kids. They’re responsible to pick out books and other small toys that need to come along. This is another time when you only want to bring what’s needed. The kids will do fine coming up with things to do; you don’t need to surround them with stuff.