It might not sound too appetising, but currywurst has become a German street food sensation that's been around since the early days of the Cold War. It's a simple dish: sliced up sausage slathered with curry-flavoured ketchup. Heat varies from mild to 'holy-crap-my-tongue-is-melting.' It's usually served with chips, and goes well with a tankard of ale.
Germany is famous for its beer, both its quality and its quantity. A German beer stein is usually at least 2 pints, so you'll need to watch how much you drink. Centuries-old laws specify that German beer can only contain water, malt, hops, and yeast. It's worth travelling to different regions, as each tends to have its own speciality. Though you might be too drunk to notice.
Turkish immigrants form one of Germany's largest minorities, and they've left their mark on the culinary landscape. Doner kebabs are available in stands all over the country and are amongst the finest in the world, comprising of sliced lamb meat wrapped in bread, and served with sauce and salad. It's the quintessential late-night snack, but you might also find it in the odd restaurant or two.
If you have a sweet tooth, Germany is something of a paradise. Black Forest gateau is a decadent mix of chocolate and cherries, streusel kuchen is like sublime coffee cake, or you might go for a classic Berliner (jelly doughnut). You're likely to come back from Germany with a much tighter belt.
The Rhine river in the south of Germany produces some quality white wine, and is particularly well known for its Riesling. You can visit Germany's picturesque wine country, or simple enjoy a glass (or bottle) in a restaurant of your choice.
This is a broad topic, without doubt, but there are so many meat dishes in Germany that we could write about them forever. There's a massive range of wurst (sausage), and meats like Black Forest Ham and incredibly robust steaks. The meats available and how they're served can vary from region-to-region, so if you're a meat-lover it's worth travelling around.
Another broad topic, but Germany produces some spectacular baked goods. It's signature bread is the pretzel, but it also makes beautiful loaves and cobs that go well with other meals or are substantial enough to be a meal unto themselves.
Germany is a multicultural country, so in bigger cities you'll find plenty of world cuisine (Chinese, Japanese, Thai, Polish, Indian, Italian, French, Spanish, Greek, Turkish, and so on), so you're bound to find something that suits you.