For the shopping cart system, like another commenter said, if you want that experience, you can go to Aldi in the US and other places. In the US it's just a quarter, and it's a way to have customers return carts themselves. If they don't, someone else that's shopping will do it for the money. You can get like an extra $1 while going to Aldi just by returning carts if people feel lazy that day. I think it's a system they have in Germany as well.
If you haven't gone to Aldi yet, it's pretty spiffy. They have some stuff other people don't, and is a good source of German food, alongside most staples people need.