It may be too late for you, but in anticipation of the backseat bloodbath we taught "punch buggy" as the "love bug" game. Instead of beating each other, the person getting the tally calls out "LOVE YOU (insert color of VW bug)!" The tally runs for an entire day (sunrise to sunrise), person with the most love / tallies wins. If someone mistakenly calls out a love bug (wrong make or color), they lose all of their points and have to start over. The 6-year-old has come back from just such a situation to win (beating out both of his parents). It gets quite competitive, passing dealerships isn't a problem - it's a point generator, thus far no friends have complained about not getting to punch / getting punched...and our minivan is completely full of boys.