In the effort to imagine what a future massive grocery store would look like I imagined Future-Mart. Instead of picking items from store shelves a customer would wave a charge card over an item's shelf display scanner for instant purchase that a self-driving grocery cart would pick up. Items purchased could be gathered and delivered to a check stand with a robot arm with a scanner in the hand (distant cousin to the Canadian Arm from space shuttle times) for redundant checking or for those without a charge card and deliver them to the front of the store or electric car in the parking lot.
Rather than self-check out registers an alternative would be for a register robot arm with bar code scanner built into its hand to place items into a cart while tallying the costs simultaneously.
Future-mart might be more practical though and simply let a customer place everything into a cart and at the register all of the items would be tally’d in the car instantly because each item has a radio frequency transmitter or another form of very short distance neo-RFT identifier that the register recognizes. A customer would initiate the process with a charge card and a receipt would print out with a list of all of the items purchased before the cart drove itself off to follow a customer outside. The cart would be made to have a box set in it that would lift up or slide out with the goods at delivery point.