Imagine the big box stores open showroom-type stores.
It looks just like a regular Walmart, but the boxes are empty, the fruit is plastic, the TVs are models, and the bottles are just for looks.
Just have the app scan your code, okay the purchase when you're about to leave (or later) and they'll deliver it as soon as possible. Or tell them to deliver it to your car in the parking lot if it's immediately available.
Anybody who ever shopped at a Service Merchandise knows what I'm talking about. Just without the clipboards.