You then scan items as you pick them off the shelf - if you're really prepared you put the item directly into a bag you brought with you.
Payment is then a case of walking up to the till - human or machine - and scanning one final barcode. Your order is presented to you for a final review then you tap your card and leave.
Arriving at the till and paying instantly means my entire queuing experience is over within 5-10 seconds
(Unless you get subjected to an infrequent random poll of your items but these are worth the occasional hassle)
Hopefully you get something similar implemented!