Dismembering Their Policies

I am at a bulk purchase store that requires membership. I am purchasing a number of items for my household, as well as some snacks for myself which I want to pay for separately. I’ve set these in two piles accordingly, separated by a divider.

Cashier: “Welcome! Can I have your membership card?”

Me: *Gesturing* “These ones are both mine; I just want to do them as separate transactions.”

Cashier: “Oh, unfortunately, with a [membership], you’re only allowed to do a single transaction.”

Me: “Okay, so then, if you want to put these—” *indicates my personal items* “—aside, I’ll just come back in and buy them later.”

Cashier: “I’m sorry, what?”

Me: “There’s nothing stopping me from coming back, right? Like, my membership isn’t going to be denied at the register if I come back in five minutes and make another purchase? So go ahead and put these aside and I’ll buy them another time.”

Cashier: *In a huff* “Well, I’ll put them through this time, but next time, you need to do them as one transaction.”

Me: “Okay, sure, thank you.”

I get that you have a policy in place to stop people buying things for “non-members” and paying separately, but don’t get mad at me for pointing out the unenforceable nature of it!