hi luckylady, I am in south Germany at the mo, but spent a year in the same area as you.
When you get used to it, you can get most things believe it or not! I am currently on a few weeks in the UK, and will be taking back to Germany: nail scissors (my children keep losing them and they are RIDICULOUSLY expensive in Germany), Rice Krispies x 100000, Weetabix (cheap), English jaffa cakes, tea cakes and other assorted tea things (yum), suet for suet puddings, golden syrup for suet puddings, real baked beans (with the authentic unhealthy added sugar taste), chocolate coins (beware, the German ones are usually toffee!), bicarb of soda and cream of tartar SEPARATELY for scientific experiments and the odd bit of cooking, and English sausages and bacon (thick cut).
The best secrets in Germany are; the bread, when you get used to it; Apfelschorle, which is apple juice mixed with fizzy water, no added sugar, and strangely addictive; the good quality meat; the cheap supermarkets Lidl, Aldi, Pennymarkt etc, quality is usually good; the Turkish supermarkets and fruit shops (cheap Turkish fruit).
In the posh supermarkets, beware of the famous shop dragons, the ladies who will scream at you for having the temerity to request a receipt (happened to me recently), or ask to look in your bag (I refuse on principle). It is worth knowing that in supermarkets, you have to demonstrate ostentatiously that your trolley is empty (eg lift up all your bags) as you pass through the checkout; it is bad manners to delay the queue by packing your groceries in bags (just hurl them into the trolley); any handbag larger than a clutch may provoke suspicion that you are a shoplifter; and when they say a shop is closing, they expect you to leave immediately.
I really enjoyed my time in northern Germany, and met loads of gorgeous people. Hope you have a great time there too!