You know how the wheeled legs of an ambulance stretcher automatically fold up when the stretcher is pushed into the back of the ambulance? It'd be cool to use that same concept for a personal shopping cart in your automobile.
So, the car (a hatchback style, or Minivan/SUV) would come with it's own shopping cart. The cart could be branded too, so you could walk through the grocery with your <insert brand> cart - good advertising.
Everything in the store would happen the same way. You'd check out at the cash register, they'd load you bags into your cart. Then you'd go to the parking lot, open the hatch, and just push the cart right into the back of the vehicle, and close the hatch.
I guess you could then wheel the cart into the kitchen at home, but the wheels might be dirty. Anyway, it'd save unloading into the car, putting the cart into the cart bin, etc. And if it caught on, the stores wouldn't have to have so many carts & people dealing with the carts...