LOL!
The supermarket should catch on to this to make the shopping experience more interesting. Let's see.
1) paint all carts with metal flake lacquer. Add some body panels so that you can include body striping and some airbrushed murals.
2) Gold-plated wire spoked wheels.
3) White wall tyres.
4) A really kick-a$$ stereo system. Okay, this means that the shopping cart will need a car battery.
5) Some hydraulics.
6) leather-wrapped cart handle.
7) Thick, white shag carpet lining for the basket portion of the cart.
Just some ideas off the top of my head.