I too collected Hot Wheels as a kid, and still have 50 or 60 of them in storage somewhere (all opened and well-used, unfortunately).
Since my playing card collection has focused primarily on decks with custom/non-standard courts, I also have a "side-collection" of sorts, of objects other than playing cards with images of custom courts on them.
These include:
* clothing (t-shirts and neckties, mostly)
* greeting cards
* wrapping paper
* refrigerator magnets
* a Playboy mag with a playmate posing as the Queen of Hearts
* a set of reproduction birth certificates of the Beatles, with the boys as Kings
* a chess set where each piece is a playing card
...and much, much more.