Beachcombing is one of my favorite activities. I love collecting sea glass, shells, agates, driftwood -- just about anything really! The photo above is part of my collection.
I haven't done a lot of collecting in the Bay Area, but with a little research I came up with a few suggestions:
- The Albany Bulb near Eastshore State Park in Albany
- Stinson Beach in Marin County
- China Camp State Park in San Rafael
- Ocean Beach in San Francisco
If you want to head south of San Francisco, Pacifica State Beach
and Montara State Beach
would be good bets, as well as many beaches in Half Moon Bay
Your luck will depend on the tides, the weather, and how many people have picked over the beach before you. Quiet places where there aren't a lot of crowds will be more fruitful. You'll have the best luck going at low tide, or after a winter storm. The beaches are also less crowded, and less picked over, in the spring and fall.
If you're an avid sea glass collector, you might be interested in the guided tours offered by Charles Peden: By the Bay Treasures
If nothing else, his web site might give you good hints on where to go, since he's an expert on beach glass collecting in this area.
Have fun looking.