Well you'll easily spend a day or two walking around Krakow old town when you get there and both Auschwitz and the Salt Mines take up most of a day so that's 4 days gone. There's also the Tyskie Brewery which I've always wanted to check out so that might be worth looking into as well as a few museums.
Most of the "sites" in Krakow are what makes up the old town. All of the old historic buildings, the Wawel (castle), the markets, the main square, that's all in the old town so that's why I'm assuming you'll spend at least a couple days walking around there and soaking it all in. It's very vibrant, tons of restaurants as well as good shopping. One thing that YOU MUST DO is go to the jewish district and get a zapiekanka:
It's literally the best. There's tons of variety too so there's a kind for everyone although you can't go wrong with the original, mushrooms, ham/pep, cheese and ketchup. There's basically like 5 or 6 little vendors in the same building that sell them and there's always a line but it's worth it. This place:
Outside of that, the best part about Krakow in my opinion is the night life. Going for dinner and drinks in the main square after the sun goes out is great as it's circled with patios. After that if your up for it Krakow has some really great nightclubs and as long as you stay in the touristy area (old town, near the main square) english will be fine and no one should bother you. The best part about it is the exchange rate. Not only is alcohol super cheap (Bottle service is 40-200 zloty roughly for a bottle depending on the place, beer and drinks are also super cheap, both in bars and at the grocery store) but the exchange rate is roughly 3 PLN to 1 CAD so you can seriously go crazy if you'd like. This exchange rate also makes food at even the fanciest restaurants pretty cheap and as for clothing the domestic brands are cheap but anything international costs the same.
Krakow's metropolitan area is roughly 8 million people I believe so there's a lot to do outside of just the normal tourist stuff, it just depends how comfortable you are off the beaten path and what floats your boat. Zalkopane is also a cool mountain town not that far away. Worth checking out.