Every time I check out at a Kroger store I tell the cashier that I would like to get a membership card. They don't require you to give a phone number until you register the card after the checkout - which I don't do because I already got the benefit of the card at checkout. This won't work at stores that require phone number first, and still leaves open credit card-based tracking - for that you actually lose the few % cash back if you want to use cash instead.