The Mercadão — the central municipal market — is one of the more useful stops in the city centre, and also one of the more enjoyable. The ground floor has stalls selling tropical fruit, vegetables, dried goods, local cheeses, and cured meats. You can find banana-da-terra, maracujá, jabuticaba (a grape-like fruit that grows directly on the tree trunk), and other produce that does not travel well and is therefore rarely seen outside Brazil. The quality is good and the prices are lower than the supermarkets.
The upper floor has a food court of small restaurants serving the kind of lunch that workers and students rely on: rice, beans, stewed meat, farofa, and fresh juice, all at prices that will seem absurd by European or North American standards. It is busy from about 11:00 to 14:00. If you are in the city centre around lunchtime, there is no better or cheaper option.