I have only been to Dusseldorf & Koln, however, I did want to tip you off that if you're at a beer garden, you might witness the disconcerting practice of deep throating sausages.
Couple of places I was at, if you ordered what was basically a sausage dinner plate, you got a tiny roll, some cabbage or kraut, maybe some potato salad-ish thing, and one or two very large sausages. People all around me skipped the utensils or the futility of trying to put the thing in the tiny roll and just picked it up with their hands and started gobbling.
When in Rome... or Hamburg.