"Sorry, I don't have it with me" gets me about 50% of the time, so its a wash. Some places where they absolutely insist on the card, like Wegmans, I just don't go there. You can take a real bath in some of those places when ALL their products sales are only on the card and the other choices are jacked up to make their shit look cheap.
I use a card once in a great while, when they have "ten for ten" sales, I'll stock up. With a card account I have at a certain store, but rarely use.
When I know I'll save a pretty good chunk, I use it, but I don't use it for everyday buying. I know if my stuff will ring up much cheaper, and if its only fifty cents or a buck, I don't volunteer the info.
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I got all pissed off at WalMart today, ringing up my own shit. This crabby old black bitch come stomping over to help me ring the shit up, because it was giving me static about putting electronics in a bag, and I told her they should knock seven bucks off my purchase, because I'm doing the work of a cashier for a fuckin hour trying to ring up my own shit.