I'm curious as to why you think none of the buildings around you are going to be standing after an earthquake. Even in (or especially in) extreme active seismic zones of California, I don't think the buildings just collapse into rubble, most, if not all of the buildings have to meet minimum safety codes. Sure, they might not be a safe to live in afterwards, but I don't ever recall seeing a residence completely demolished from a single earthquake. I just say that because that kind of thinking severely limits your possibilities, and could be dangerous if you've already written off the possibility of storing stuff inside your condo. If everything does collapse, why would you even bother to shelter in place?

One upside to earthquakes (if there is an upside), is that even if your building is severly damaged, there's still a good chance that at least some of the stuff is recoverable. It might be crushed, it might be dirty, but at least it's not contaminated by flood or strewn all about by a tornado.

Carrying a weeks worth of food and water is probably not possible. Hitting the local markets, I dunno about that. Being around a bunch of desparate people fighting for food and water, right after a major catastrophe isn't the first place I'd want to be. I'm not even going to get into the fact that taking stuff from a market is stealing, plain and simple. But I won't push it any further except to say, how would you feel if while you were out looting, someone passes by your place or car and decides to take what little supplies you have left?

If you're really convinced that nothign around you will be standing, the only option is to find a place within walking distance (since there won't be any roads), but far enough away and stable enough to still be standing after the Big One. Maybe a friends basement?

EDIT: Now that I know where you're located, it's easier to see the situation. Anything short of SF breaking off and sinking into the sea, there should still be ways of exiting. Freeways might be down, but there are plenty of roads and other paths out. This is one situation where I think a bike might come in handy.