I always managed to find free street parking near Jack London Square on the weekends, whether it's going to Yoshi's for jazz and sushi, Barnes & Noble for book browsing, or the cinemas for a movie. Perhaps it's pure good luck. Get on 2nd Street - I often can find some spots near Bed Bath & Beyond (590 2nd near Clay). If you can't find any, there's always the pay (multi-storey) parking lot across from the cinemas.

Remotely yours,
Yoosh