I worked as a cashier in Publix, just about the cleanest store you can find. Problem? People who come thru the line. Sneeze, sniffle, kids, babies..... . Touching the belt, touching the metal sides, the boards, the machine that you punch the numbers in. And you were worried about the grocery cart, lol. I cleaned my counters, belt and everything else often. And if I had a customer come thru that sneezed or sniffled all the way past, would try to discretely hold the next person in line up from touching the machine until I could wipe it down. That might be why my line was always busy, beside the fact that I was also very fast. I also had fewer colds over the years than anyone else I worked with.
I don't worry about the carts unless they are sticky. I pull up the plastic part of the seat so nothing falls out of that section and put my purse in there, and loop the strap over the handle. I don't turn my back on it while shopping. NOR do I leave it open and money hanging out of it. Yes, I have seen that done, all too often. Hey, just stamp stupid on your forehead, lol. Bag your produce. In fact, bag your meats, too. They will be nicer when they thaw in your fridge. Wash your fruit and veggies before cooking and eating. Wash your hands. You lived this long....and you were not all that germ conscious as a kid.