Appropiate shoes,antiskating,high boots are recomended.
Clothes that can keep you dry,food twice the time you plann to spend inside the cave.
Toiletries and Medical Supplies: First aid material is necessary.
Miscellaneous: Always use a handlight and a backlight.
At least one person must take some kind of generator.
Headlamp is a must,the main item I think.
Batery refils,twice the time planned to spend in.
Water proof container for food and the generator.
Clothing/Shoes/Weather Gear: Like every big city, you are expected to dress nice, specially if you are planning on going to the nice restaurants I suggest here. It doesn't mean you should dress up really fancy. You can wear casual clothes, and jeans, but try not to wear those with your old t-shirt.
Before going to anyplace in Brazil, check to see if you need a Visa. Citizens of the US and Canada need visas. A waived country list can be found at the link below:
Brazil Visa Information