How Much Money Should I Take On A Trip To San Fransisco?

My boyfriend, his friend and I are planning a trip to San Fran. in the winter. They are going more to check out the bike scene and I'm probably going to be the one shopping/ getting souveniers. I don't think we'll be eatting fancy meals but we will have to eat. Around how much should I take for spending money? (not including hotel and train ride to S.F.)