If I had a grocery store, I think I'd set it up that the behind-the-shelf area was hollow, and accessible from the basement. Clerks would stock the goods from the back, the way the milk refrigerator usually is. This would happen perpetually, so all you'd notice is that the supply of goods on the shelf never seems to run out, no matter how much people are buying it. There's probably some reason that supermarkets don't do this, but I can't think of what it is this morning.
Also, why don't supermarkets ever have a second floor? (Okay, many of them do have an upstairs office for administrative purposes, but the customer-accessible area is all on ground floor.) Stairs would be a bad idea, since most shoppers now use carts, but a ramp up to the top would work. Stores could have more selection on less real estate. What, are people too lazy to push a cart up a ramp?