You place an order online or on your mobile phone while you're at work, or on the bus. After you decide on your order, the app generates a unique code. The grocery store is now replaced with an automated warehouse, with pickup or drive-through windows. You walk up to a window, scan your unique code that was generated earlier, swipe your credit card to confirm, and the warehouse automatically picks your items and out they come in bags. You toss them in your trunk if it's a drive-through, or just carry them away if these are city center stores.
Optionally, the store could have a little room to pick your own fruit and veggies, in case you prefer to see them.
This makes the whole process a lot more flexible. You could even remove the concept of placing orders and generating codes, and instead have a grocery store account for your household. For example, you ask your son to pick the groceries down the street. After he leaves, you realize you want some curry powder. You just click a button on your phone to add curry powder to the online list, and that's it. Your son doesn't even need to know, he just shows up at the window, scans your family card or enters a password, and out comes your groceries, including the newly added curry powder. After he gets the groceries, the online list clears.