I had a cat back in college named Rusty who used to love riding in the car. I would take the bus to my parents' house to borrow their car, go back to my apt to get my laundry and Rusty and off we'd go. He liked riding in the car so much that when I permanently re-homed him to my parents' house, he would get in anyone's car, if they left a window down or a door open. So many times people--friends, tradespeople, anyone--would leave our house and get half-way down the block only to turn around and bring Rusty back! He would wait at the foot of the driveway and when you got home from wherever you'd been, you'd have to stop and let him in the car and drive him up to the house--a whole 20 feet, probably!. One time he got in the back of my Dad's pick-up truck--luckily my Mom saw him and was able to flag my father down before he got too far down the street. Old Rusty was quite a character.
Interestingly, he was in a car when he died--we were taking him to the vet to have him put to sleep (end-stage FIV).