Cookie sheets with a rim make a great "desk" for drawing and writing...and for holding some new fun magnets. Stickers, postcards to send back home (get your stamps now), new fat crayons, a couple of new matchbox cars, little "stained glass" coloring books (Amazon has these), and don't forget tape to stick them on the windows. Write their name for them on whatever they create, tell them they can give it to grandma when they see her.
Have all this stuff in a bag they can't see in, and take out something new every few hours.
Stop often for a diaper change and a run around! I know that will add a couple hours to your trip, but it will make the trip more pleasant. And a good heavy lunch will make for a longer nap time.
Goldfish, dried fruit, sippy cups for water. If you can't reach them easily from the front, whoever is not driving should sit in the back with them. They get a real kick out of that!
and you'll need to stop a few times so they can burn a little energy. McD's Playland worked for mine. Just let them run around and play for a half an hour. I have done this a few times. At 2 and 3 they still sleep alot in the car. We also tried to travel at night to avoid traffic and because the kids slept the whole ride.
