Despite the general thought that Spanish produce is cheaper in Barcelona's markets than in its supermarkets, sometimes it can be convenient to shop in a store, especially when you are looking for items not usually found in the market, or when the market is closed.
For example, in Passeig del Born you will find a supermarket known as De Tot al Born. Although it is a small shop, it boasts a factor that is extremely rare in this bustling city: it opens on a Sunday. This is really useful to know if you are near the area, especially as it is a well rounded store selling fresh fruit and vegetables, alcohol and refrigerated goods. It also has a bakery, where bread and pastries are produced in-store every day.
Carrefour in Las Ramblas is also a useful store; it is one of the biggest supermarkets in the city, boasting its own pharmacy, which is always useful to know.