When, and for how long, will you be here?
Chinese New Year celebrations start the first week of February, and you should eat Dim Sum in Chinatown at least once while you are in town, regardless.
I have a lot more food-related suggestions, should you want them.
Fisherman's Wharf/Ghirardelli Square has some nice shops and pleasant strolling. (Ghirardelli Chocolates is there. I also happen to like "Lark in the Morning" a music/instrument store where you can buy just about any kind of weird instrument. I get my bagpipe reeds there.)
Haight-Ashbury is the former hippy area of the city - much less so now, but still definitely has its own character, and is home to tattoo/piercing parlors and the like, as well as some good restaurants (Massawa is a good, but very cheap Ethiopian restaurant there, for example.)
If you'll have access to a car, I suggest heading north and east from the city to visit wineries in Napa or Sonoma. Sonoma, especially, is less than an hour from SF. I can sugest some specific wineries if you want.
Edit - just realized you're from Vancouver, and probably have really good Dim Sum there anyway. Still, it's one of my favorite SF activities.