Just attended a going away party for a friend with two toddlers who is driving across the country with them. Some of the gifts she received to help amuse her kids in the car were rather original --
packages of colorful bandaids for the kids to stick on the windows
a small cookie sheet filled with fun magnets
colorform stickers to put on the windows.
those cardboard cards that have holes in the edges for the kids to stitch with yarn - kind of tricky for really young toddlers but still fun if they can do it.
little figurines tied with long thin strands of ribbon so mom can tie them to the car seat and the kids can play with them without losing them if they drop them.