Food:
Look out for the little fat soldier on restaurant signs, it means that the restaurant is a tourist trap that serves bad expensive traditional food. Instead visit the many italian restaurants that have excellent quality for similar prices or the places where the locals eat that have OK food for very good price.
Cheap food trick: draw a ring around every tourist attraction, move to a position furthest from any rings, there you will probably find non-tourist-infested restaurants, be prepared to order using charades unless you speak Czech.
Beer:
* I visited a beer tasting in an old brothel -> socialist worker canteen -> nightclub -> punk bar (the place were about to be demolished and the punks were helping
) I guess they still hold the beer tastings, in some to me unknown location. Highly recommended, quite cheap, very informative.
* Staropramen brewery tour, quite central, quite useless if you are interested in the art of brewing beer, possibly interesting if oyu like stainless steel and panels with buttons.
* Monastery in the hills above prague. Interesting ales.
* Do try the unknown local brands, they are usually better than the famous brands (better==interesting character)
* Do try to locate a local "three pints is a lunch" lunch place, called Pivnice or Hospoda. I failed to locate such a place, maybe I did not drift far enough from the tourist attractions.