Shopping for groceries is a lot of fun in Paris. The ingredients here are fresh,and there's such variety of fruit and cheese and meats and bread and pastry. The produce quality is better than in San Francisco, too; it's shameful how bad lettuce is in California.
The trick in Paris is to buy things from specialists, not supermarkets. This means going to several different stores on a shopping trip and figuring out which boulanger has the best bread, which cheese shops are better at mountain cheeses vs. soft cow cheeses, and careful produce inspection.
My favourite place to shop is the Marché Maubert, a three days a week outdoor market. Some 30 different vendors selling fruits, vegetabls, meats (calves brains!), cheeses, pastas, middle eastern specialities, and, oddly, suitcases. The two or three permanent shops there are quite good as well. My Parisian restauranteuse friend Evelyne was kind enough to go shopping with us the first time and show us the ropes. Quite easy; afterall, the vendors want to sell to you as much as you want to buy.