Most non-player characters can be bartered with. In addition, almost all friendly towns have 1 or more merchants with a substantial and replenishing selection of items for sale and a large amount of caps. The general store is the most basic shop and can be found in most settlements. Doctors sell medical supplies and are also present in most towns. Weapons and Armor merchants can be found in larger settlements such as San Francisco.
Generally, the further south a shop is, the better stocked they tend to be. The stores in San Francisco have the most extensive inventory in Fallout 2. Shops specializing in other wares can be found.