Nice one. I keep mine on the floor of my backseat and easily reachable from the driver's seat. On the floor so it wont fall down from the seat. Some of my best shots have been from the car!
@grannysue I usually have my camera on my lap when I'm in the passenger seat but I do put my longer lens in the cup holder many times to have it ready.
He just has it handy for when we stop.
Love the cup holder idea!