Get a burrito in the Mission, play video games in Chinatown, shop for records at Ameoba in Berkley. Return to the Mission for a paleta. Late at night go for donuts in the Castro. Talk to strangers. That ought to cheer you up!
Damn...I miss Ameoba Records! That place was awesome. As for SF, don't forget Mel's...best malted milk shakes around. And Miz Brown's Feed Bag...awesome banana pancakes.
I spent 4 years living in SF proper, and then another 4 on the outskirts (Daly City and Richmond). It can be dirty, and the traffic absolutely sucks, but it does grow on you. I now live in CT, and I miss the place every so often. Sometimes the wife and I will catch a documentary on about SF and just watch it and sigh.
Oh...and as far as chocolate, no disrespect, but Ghiradelli pretty much sucks. See's candy is a lot better.