Instance #3,428 of "however did those of us who grew up in the 1960s ever live without this?"
Well, to be honest, on our long family road trips (NY to Northern Michigan) we piled into the family station wagon and had the back folded down and outfitted with mattresses and various toys and games.
Since today that is outlawed and the kids have to be strapped into carseats for the duration the DVD player is probably a welcome solution. (Unfortunately it turns the kids into even more TV addicted zombies than the earlier, albeit less safe, option.)