I had a ton. I loved to set up a track on a book case and let the car go down it over a jump. If that makes sense. I played with my neighbor when I was younger on his slide. We lost a lot of cars that way because he had tall grass. haha.
My son has mostly Hot Wheels collection but someone gave him Matchbox cars with different states (USA) theme on it. Since we don't live there, I don't think he can complete that collection. He has them stored in a toy car suitcase we got from ToysRus over there.
I've quite a few tossed away in boxes up in my closet. I've collected them in various spurs over the years and I dont have full collections, got a few that are close but I think out of all the series' I have, hardly any of them are 100%.
I also used to work with a guy who collected only ones that had Surfboards attached to them. He said that the oldschool ones with Surfboards were considered health hazards and were discontinued. So yeah, any time I see the new ones with surfboards I cant help but think of that oddball variant collection.