Restaurants, bakeries, gas stations, and everything at airports or train stations is open on sundays in Germany.

Last time I went to Germany was...2009? I grabbed something to go at the airport and hit the road for my destination in central Bavaria. After I checked into my hotel, I hit six entire towns where everything was closed. It was around 6-7pm on a Sunday. Which is a hugely popular eating out time for families in the States. I finally found a Kebab place that was open and stuffed myself to the gills I was so starved. The rest of the week was perfectly fine. The next Sunday? Same thing, only I made sure to have a couple pre-made sandwiches in my hotel room and some breakfast meats I stored in the fridge from breakfast the previous day.

As a traveler, Germany on Sundays simply sucks.

Where are you having these problems?

International travellers tend to arrive by plane or train (as Derbasti says), you can buy something from there. Or from a restaurant.

The only problem you would have is with supermarkets away from the train station or airport.

The Middle of Bavaria. Of course the airport had food. But I was 2 and a half hours away from an airport by autobahn. Every restaurant for dozens of kilometers around was closed.

I asked my hotelier about it and he just shrugged and told me where to get some kebab three towns over.