I would be inclined to go in without a mask. If they aggressively insist, will smile sweetly, don one. fill a trolley with frozen food, get to the checkout and then realise in horror that I’ve left my purse at home and leave with a promise to return, and leave them with their perishing pile.
What a horrible thing to do, it’s the workers on the shop floor who’ll have to deal with your behaviour, adding more workload to them, many who are in minimum wage. And they’d just put in back in the freezer, they wouldn’t bin it!