I've found that very often the cashier will swipe their own discount card if you tell them you don't have one of your own. You can also, in practice at Safeway

I've found that very often the cashier will swipe their own discount card if you tell them you don't have one of your own. You can also, in practice at Safeway at least, ask for a new one each time. I used to collect them just for shits and giggles, I had dozens before I got bored of it. As a tracking mechanism, they rely on the customer cooperating and using the card as intended.