We just did a 13 hour ride with our 7 and 5 year old. They each had 3 books, a small toy, and a bingo game. They were fine. They looked out the window, we talked and told jokes most of the way.
They were fine on the way there and the way back with little to do. And believe me, my children are INTENSE creatures. There is just something about being in the car and being able to look at different landscapes that works. We saw farms, mountains, The Worlds Most Awesome Flea Market (Thank you, God!), parks, hills, trees. They were cool with it.