I live in the Friedrichshain section of Berlin Warschauer U/S-Bahn station). Formerly part of East Berlin, Friedrichshain is known by Berliners as the "Alternative" neighborhood: a kind of bohemian young person's hang out. It certainly has its share of young people, music venues, clubs, bars, restaurants, and cafes; but, it is also rich in history. From its working class beginnings in the 1920s to its current trendy cosmopolitan sophistication, Friedrichshain has been a magnet for eccentrics and the avant-garde.
Simon-Dach-Straße is the heart of Friedrichshain where one can find the latest in fashion and the current food craze. It is one of the liveliest places in Berlin, and for its residents, it can be very noisy from all the human activity that occurs on the streets. In the summer months, I need to wear ear plugs to sleep.
On Saturday mornings, I recommend the outdoor food market located at Boxhanger Platz (a block from Simon-Dach Straße and Kopernikusstraße). Try the fish stall where you can order fresh grilled trout. The trout (die Forelle) is the best I have had anywhere in the world, no joke! You can eat it on a bun or with a small salad. For dessert try the stall that only sells Kuchen (a type of German cake) baked right there. I prefer the Pflaumenkuchen (plum cake). Very tasty (Sehr Lecker). Also, if you're in the mood, pick up a bouquet of flowers. One thing about Germans, they love fresh flowers and there is almost no shortage of flower sellers. You can find flowers for sale at almost every U/S-Bahn station, shopping arcade, grocery store or open air market.
On Sundays, Boxhanger Platz has an overrated flea market. Lots of tourists and junk for sale. Avoid it if you can. Instead, head to a restaurant for a Berliner Sunday brunch. You haven't had brunch until you've done it Berlin style. It's something! Brunch is all you can eat, and includes meats, cheeses, fruits, vegetables, breads, salads, fish, pastries, cakes, pastas, casseroles, etc. The price of brunch usually includes a glass of sparkling wine and/or juice. Brunch starts around 10 am and ends around 4 pm. Prices range from 7-10 euro. Go early and go hungry.