Brazilians dress really casually unless you are among the jetsetters.
Are you going to a beach or to a city?
You will get the best bikinis and Havaianas (or Ipanemas) there - the ones we wear in Europe will look frumpy in comparison. (I had my Havaianas customized with little jewels there.) It's also a great place to buy big semiprecious jewels.
Brazilian dressing is all about statuesque bodies, great hair and great tan and slim sandals. None of which are easy for non-Brazilians.
Low end Brazilians shops are all about polyester. If you prefer cotton, take the basics - shorts, skirts, vests, t shirts, sundresses with you.
Sun is very strong - take a sunhat and the the highest-SPF sunscreen you can find with you. If you are travelling with children, take UV protection suits for them.
Middle class and upper class Brazilian women are impeccably groomed and manicured and pedicured - many of them go to a salon weekly or even more frequently and have maids who iron even their underwear. Having your nails done there is very inexpensive.
Some big cities are very dangerous - several friends have been mugged in Rio. I would not take any even remotely valuable things to the beach.
If you go to Bahia want to do candomble, take an all-white outfit.