M.H.
My in-laws are 6 hours away and we make that drive about 4 times a year. I pack a bag of toys and snacks and books for the kids and just swap toys as they get bored. We also plan the trip so that we have extra time for stops along the way so our oldest can run around for 5 minutes or so at least once during the trip. We don't have a DVD player in our vehicle but I'm sure that would be a big hit.