FastCheckout

At the grocery store the cashiers and their expensive scanning equipment are often idle while people dig for pennies etc. and other customers waiting in line go nuts. To fix this problem let the "cashiers" just do the scanning. When everything is scanned the customer gets an identifying token from the cashier (card with barcode or RF-ID tag). To get really out of the store the customer presents the token at a reader (connected to the stores central computer) and pays there. After that the store gate opens and the customer can leave.

The readers are fairly simple so the stores can have many of them and slow customers don't cause congestion. There could also be a few "everything accepted" lanes for people who insist on writing checks, like the "all vehicles" lanes on highway toll booths, and EazyPass lanes for frequent customers who just show their face to a camera to have the purchase deducted from a bank account (let's say up to $100 to limit the risk).