There are excellent supermarket chains from hypermarkets to 24 hour convenience stores. The range and quality of fresh produce is truly excellent. A little point to watch is that these street markets close the streets they are held in, so check that the flat you are renting is near to but not on one of these streets. Meat is a very important part of the Brazilian diet. It is of excellent quality.
Fish is also good but relatively more expensive.
Portuguese Learning Portuguese is vitally important if you want to enjoy Brazil. It opens the country and all its delights to you. Without it you will miss the culture and the natural friendliness of the people. It took me about three months to feel happy in the language in my work environment, though a little longer to become socially adept. As always the best approach is not to be afraid to speak even if you know you are making lots of mistakes.