I read somewhere that a cart in the grocery store has more germs on the handle than, well, it has a lot. A close second was the bowl of community peanuts on the bartop- seriously.
There are actually stores that have mini-carwashes for carts, a cartwash if you will. Our store just has Clorox wipes for those so inclined.
Of course you could go the route that our celebrities did. Guess who!