So here's my entry - Max giving us the big cheeeeese pose. Love him.
We have a box next to his car seat filled with toys and books which Max can reach across and rummage through - this is rather new, before that the toys were all over the back seat.
There is usually a balloon in the car. This keeps him amused for a good 10 - 15 minutes. It is best to keep the balloon tied to something so it doesn't wonder into the front or out the window.
Singing - and most popular and what usually lasts at least 10 minutes is Old MacDonald! I sing my own version (basically a shorter version) and I pause to ask Max what animal was on the farm and he will make the animal noise - I get a clap when I get it right!!
Anything longer than 30 - 40 minutes in the car and the boy nods off