In Argentina things become a bit more expensive than countries in the north of South America and so generally you will notice travellers cooking for themselves much more. In Mendoza we bought some really nice bread (finally decent crusty French bread and not sweet!) and fillings and made tasty sandwiches. There is also a really good food market, the cleanest we had seen to date on our travels! It sells every cut of meat imaginable including tongues, different herbs, fruits and vegetables and fish. You should be able to find some good ingredients here!
People are friendly in Argentina and many stop and asked us what we were doing etc. so it makes a trip to the market nice when you can chat with locals along the way. They also sold a good array of empanadas here which we bought a bag of for one of our day trips.