Fill your cart at one of the points of sale affiliated with the service, scanning the barcodes of the products you are purchasing yourself as you put them in the cart. At the end of your shopping, go to one of the designated checkouts. You will thus be able to pay for your purchases without having to remove your items from the cart to place them on the checkout roller, saving time when paying. Not only that: DIY checkouts often don't even have a queue!