My family game is Racing Demon*. It’s a fast, vicious game played with several packs of cards, which get strewn across the table in the course of play and have to be sorted out at the end of the round. Therefore it’s useful to have cards with distinctive backs. It’s rough on the cards: therefore it’s useful to have a lot of cheap packs.
Over the years, I’ve collected quite a few packs of playing cards. If all my aunts and uncles and cousins turn up at once, I’ll be ready. It’s become a bit of a thing. At least this means that people always know what to give me for Christmas. Playing cards, or books about playing cards. This was one of them.
*Rules vary: that link was the best description on the first page of Google, but in our house it’s ten points for a king, none for going out (going out is advantage enough in itself, for heaven’s sake!). And adding an extra card to your hellpile if you went out in the last round is not optional at all. You do get to take it off again if somebody else goes out in the next one, though.