Currywurst! (Because...Berlin)

If (when?) you end up in Berlin, the one things that can't be passed up is Currywurst.  From Wikipedia

a fast food dish of German origin consisting of steamed, then fried pork sausage(German: Wurst) cut into slices and seasoned with curry ketchup, regularly consisting of ketchup or tomato paste blended with generous amounts of curry powder, or a ready-made ketchup-based sauce seasoned with curry and other spices

For you ketchup-averse types, this is - seriously - awesome food.  Surprisingly light (to be fair, for what it is, its surprisingly light :-) and immensely yummy, one of the best places to get it is at Krasselt's (Steglitzer Damm 22) where the lines are usually long, but move rapidly. (And yes, thats +Heinz Gies over on the left above)
Also, FWIW, you're supposed to get it with a roll (which you use to sop up the ketchup/sauce), and (hot) chocolate milk to drink.  Check it out...