As a german in the US, I suddenly felt as if I had a OCD about the way to bag stuff. Store employees were more or less dumping things kind of randomly in bags without sorting by weight and by robustnes of the product. On the other hand declinining help with bagging seemed to be kind of unusual.
Other differences I noticed: Time at checkouts was at least 2-3 times longer than in Germany, even at the better german supermarkets cashiers are much faster. Also, in Germany I never encountered cashiers to comment on the goods I bought (I don't mind much, but it still felt a bit like an intrusion in privacy. I once bought a glass of Ghee - a common ingredient in southern german cuisine - and the cashier went on and on about how unusual it was that a white guy would buy it).