SFG is good, but you'll feel much more secure if you take a look at the Sunset Western Garden Book. The El Cerrito library has a circulating copy. The Sunset climate zone system is quite specific. You and I and everyone else on the East Bay margin from Fremont up to Crockett or so live in Sunset Zone 17. Others do, too; there's a great map in Sunset to show the zones in the Bay Area.
What I've grown during the cool season (plant very soon): chard, kale, broccoli, romanesco broccoli (DH calls it "fractal broccoli"), rapini (aka broccoli raab/rabe), potatoes, bok choy, cabbage, arugula, carrots, sorrel, fava beans, and the like. Favas are amazing: I've now grown them in every month of the year. Harvested in March (Palo Alto), June (here), September (Palo Alto 2nd time), and November (here).
What I've planted that hasn't worked yet during the cool season: beets (not sure why), parsnips, radicchio.
The City of El Cerrito has now sponsored two compost give-aways, one in October 2010 and one in Spring 2011. Driver's license or other ID with El Cerrito address was required. I missed the spring one (rats!), but we each got 2 cubic feet in October 2010. There will be a community gardening meeting--an initial meeting--at City Hall on Saturday, Sept. 24, from 10:00 to noon; this would be a good time just to drop by and get your name on the Environmental Activities e-mail list. It's how I found out about the compost give-aways.
How large a Square Foot Garden are you trying to improve? And have you checked with American Soil and Rock on Jacuzzi Street for prices? Not cheap, but excellent stuff. Westbrae Nursery on Gilman in Berkeley also runs occasional specials on organic potting soil and/or bagged compost/fine-grade mulch.
Sunset Zone 17, USDA Zone 9