>1. Require cash.
They'd have to make that very clear at the entrance to the store. This is just a guess, but I think most Swedes don't carry enough cash to even pay for groceries when they go shopping. I haven't had any paper money in years, just a few coins.
Cash is incredibly rare in Sweden these days.
But Swish (mobile payments) could work.
Cash makes up less then 15% of transactions in my country. It would be less disruptive to just close the store.
But if the store in question would accept cash, then it could at least server some of its customers. I expect it would not only be 15% of the customers. I would add those customers who are, you know, a little capable of adapting to circumstances and would actually go to their ATM to pick up some cash if they don't have any in their wallet. If not, I guess they don't need those groceries so urgently.
> go to their ATM
I think you're underestimating how little we use cash. There aren't even ATMs in some parts of town and there are plenty of villages without one for tens of miles. Nobody uses cash anymore. It's all either debit cards or direct transfers (either via and app or the bank.)
Treat it as "card not present". Write down the card number, expiration, cvv, name, and zip or equivalent. Get a signature and process it later. If you can't process it later, your system design is flawed.
2. Have clerks write down what is needed on the shelfs.