how is the best way to travel with money in south america?

shoul i use a fanny pack? or any other gadget?

Major credit cards are widely accepted in hotels, restaurants, stores and other businesses in urban and tourist areas. If you need to change dollars you can do this at the hotel or at authorized exchange facilities ("casas de cambio"). ATM machines are available at banks in addition to some shopping centers and gas stations in urban and tourist areas. Traveler’s checks are also typically accepted.
If you NEED to carry the money with you, check out the travel store at AAA, or any other store. (they sell socks with zipper)
Von Voyage!