I usually go to the Redwood City Costco, but yesterday, found myself at the Foster City Costco. The store seems smaller than RWC, and correspondingly, there seemed to be less variety of food products. For example, RWC has organic eggs in both the 18 and 24-egg cartons, where FC had only the 24. At FC, the prosciutto was Citterio (a brand I see in many stores and apparently American-made), in a single package, and the salami selection was limited. At RWC, they have Salumeria Rosi, an Italian import, which tastes very much like Prosciutto di Parma and comes in a 3-pack. At RWC, there are often a lot of Mexican products (tamales, masa, etc.), depending on the time of year, and I didn't notice many at FC.
I would love to hear what others have discovered in terms of the differences in food products (and wine) carried by the various Costcos throughout the Bay Area. For instance, do some Costcos carry a larger selection of wine, or Asian products, or cheeses, or.....???