Sometimes shopping with my wife can keep the brain juices flowing.
Create a microscopic unique RFID tags and attach them to products. So that no two tags in the world are the same.
Customers now select their products.( clothes etc.) And they simply place their cart in a big scanner( just like the ones at airport) the scanner now scans all item at once using the radio and deletes them from the system.
So with just one scan all your items are scanned and the price is calculated. You pay with your card and that's it.
No cashier. No Queue.