Convenience stores could become even more convenient by getting rid of lines to check out at a cash register. Instead, shoppers who have their credit cards on file will scan items with the store's app and drop them into a bag -- as customers already can do at six Amazon Go stores in three large cities. And at 2,500 McDonald's restaurants, a touch-screen terminal takes orders and payments. "Think of it as the ultimate self-checkout experience," Forbes magazine says.

Advances in robotics, artificial intelligence and other technologies pave the way for more stores with no cashiers and fewer workers. These retailers will automatically charge customers for food, drug store items and other goods they take, and use robots for inventory and stocking. They'll still have a human security guard, naturally. Amazon is the pioneer in this strange new way of shopping, with grab-and-go snack stores in San Francisco, Seattle and Chicago that sell sandwiches, chips, other nibbles and beverages. New York is next, says the firm, which reportedly plans hundreds of Amazon Go locations by 2021 to compete with 7-Eleven and other mini-marts.

Walmart, working to catch up, is experimenting with a cashier-less Sam's Club store in Dallas. Customers use the chain's Scan & Go app to add products to their receipt as they shop. They pay through the app with a single click and leave. Instead of traditional checkout lines, there are 700 cameras to keep patrons honest and monitor inventory. The app can provide voice directions to any item and eventually will be able to create the most efficient route through the store based on a shopping list. Walmart also is testing a no-lines concept called Check out with Me at 350 stores. Roving employees check out customers on a mobile device that sends a digital receipt via email or text – an approach adapted from Apple stores.

Kroger, a chain with supermarkets in 35 states, last year introduced a Scan, Bag, Go app that lets shoppers at 400 stores scan and bag products as they shop. They still pay at the existing self-checkout area for now, though the plan is to allow payments directly through the phone app.

Professor says: "It's not going to be very much longer in the future that robots are able to pick individual orders for customers." – Mark Cohen, retail studies director at Columbia Business School in New York

Business journalist says: "The future of retail is about making customers' lives easier and better." – Blake Morgan, Forbes magazine contributor and author

Union economist says: "The quality of customer service is going to decline as that staffing level is cut." – John Marshall of United Food and Commercial Workers International, a union representing grocery employees.