The Flash, on the Red Volvo station wagon, is a cheap plastic rolling figurine that I broke the wheels off of and stuck on with double-sided foam tape. The flames on either side of him are magnetic. I had to take him off every time I washed the car, but it wasn't a big deal.
The pink Yip Yip on the Audi is also stuck on with foam tape. He's temporary until I can find a more suitable ornament.
I just can't stand having a boring car!