Re: what to buy - San Francisco whats cheap to buy? cloths, shooes, cameras, gold?
What do you want to buy? It is a bit bizarre to simply decide to go somewhere and then look for lots of cheap things to buy. Things to think about are transporting the stuff home (clothes are a pain to have to transport) and issues around customs.
San Francisco is one of the most beautifully situated cities I think I have ever seen. The city is compact and walkable once you get over the hills! Don't waste your time shopping get out there and see it.
It is a foodies city, it is full of restaurants to suit all sorts of palates and pockets and is a joy to eat out in. Make sure you get to the Ferry Building (on a Tuesday I think) for the market.
There isn't anything that is especially cheap in SF compared to the rest of the US. I would suggest Chinatown for endless tat (and some illicit ivory!!) although there are plenty of interesting things to buy too. But what I brought home from SF was Sourdough bread (bought in the airport after security), California wine (well Napa is only up the road! Again after security), Ghirardelli's chocolate (wasn't as fond of See's Candy although I got some of that too) and then mementos from the Cable Car museum (which is free entry), from Alcatraz (which isn't) etc, clothes by request (which were a pain to have to transport but easiest way for family to buy Abercrombie and Fitch), books and some jewellery for myself, although generally I find American jewellery styles not to my taste.
When I look at it here it is quite a list

but like I said, I didn't go to shop and furthermore I wouldn't. I found that while yes you can buy very cheap stuff in the US, generally cheap stuff is ... cheap. Quality costs there too.
(BTW - I liked Trader Joe's too)
One very different thing to do in SF is to go visit the Bay Area Model in Sausilito. It is a scaled down version of San Francisco Bay built by the US Army Corp of Engineers that was used to simulate the Bay as a three dimensional model. [broken link removed]