1. Require cash.
2. Have clerks write down what is needed on the shelfs.
2. Have clerks write down what is needed on the shelfs.
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.
But Swish (mobile payments) could work.
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.)