My own tip would be to get to the Kazimierz District (The historic Jewish district) - a ten minute walk outside the city walls. It's really funky with loads of cool bars.
A few quotes from Tripadvisor:
Great place for food and drink and general ambience, very busy in summer and loads of cafes, resturants, beer gardens to pick from, all within a small area.
I found that Kazimerz is a great night out better than the old town as all the bars restaurants are located in 2 squares which are back to back. There is also a market in the middle of one square. I spent the day in a bar over looking the street then went bar hopping. a great night from what i remember.Next time i go to Krakow i will be booking a Hotel in Kazimierz.
This was the area we enjoyed most after the main square. Very busy, lively and a super atmosphere. Some really nice eating places and one which contained the best food we had tasted anywhere in the city. Great character in the buildings which although quite old, were given colour by the various shops and bars many of which have outside seating where you can watch the colourful world go by.