To start off, there are roughly 70% import taxes on all goods brought into Brazil. In general, anything you see on the shelves of your local store are going to be twice this price in Brazil, and likely twice the price based on the full retail price! The good news is that fresh food, lodging and services are all relatively cheap in Brazil, even for higher end products and services. In general, I have found Brazil to be one of the cheaper places to visit in the world, while maintaining a fairly high quality trip. Generally, trying to maintain a high standard of living in a cheaper country actually becomes more expensive.
So be aware when packing to bring everything with you. Especially lotions, creams, batteries, and sun tan lotion!
If you plan on renting a house short term, or planning on staying with friends, or you're the type to easily make friends, come prepared! It's fairly customary to bring your own sheets, and towels. If you're renting a furnished house short term, bring sheets and towels! Make sure you contact the home owner to see what is standard as well. You might get there and find nothing! Not even a fridge! When in doubt, ask a lot of questions. What you assume is necessary for a short term rental, might not what the renter thought was necessary.
While medicines are most likely cheaper in Brazil due to government bargaining power, getting a proper prescription could be extremely difficult.
While bringing batteries is a good idea, don't get carried away with electronics. Bring what you need, but avoid over doing it. Theft is fairly prevelent in most areas of Brazil, and carrying around too many valuables just entices more people to target you. Even leaving items in your hotel room may not be safe. Break ins and employee theft could hit you! If you are in a hotel, invest in the hotel safe, either in the bedroom or in the lobby. Put all of your valuables, including passports in the safe.
We would recommend not bringing or wearing expensive jewelry. Theft in Brazil is often from vary different people than you would expect to find at home. Theft is often the poor, with no alternatives but to steal to put food on their tables. These people can be fairly desperate and a little more dangerous due to this. So don't bring anything that will bring unwanted attention your way. The key here, unfortunately, is to become a less enticing target than another person.