When going on long car trips, prepare ahead with paper bags of items to be given out every 25, 50 or 75 miles — marked on a map with the location, it takes a little bit of preparation to do this but it REALLY helps young children.
In each bag put a wrapped item — usually a small toy. Then in some of the surprise packages you can add juice or a snack, stickers and a piece of paper, or something pertaining to the trip that you can talk about.