Music, coloring and a portable dvd player has helped us. Any car activity to keep them busy and not distract us from driving. Taking the dvd player out of the car is the only pain in the butt for us. If all 4 of my cars weren't so damn old, I would consider the dvd systems in the headrests.
We use to take toad trips to NY from NC to see my family and all I had was playing hide and seek with silos, water towers and bridges, and looked forward to seeing cows and horses out the window. My parents even made me listen to oldies radio stations since we didn't have a cassette player in the car until 1994.
You have a good heart and set a good example as a positive male influence in his life and he will remember it.