"I am confused why german stores close even on Fridays. What if your fridge is empty at Friday night?"
That's no problem. Since several years stores in Germany close at 20 o'clock. Every evening. On Saturdays they may be open until 20, but some close at 18 o'clock.
There may be a problem on Sundays. Only shops in railway stations and gas stations are allowed to sell provisions to travelers. But some bakeries are open Sunday mornings.