You will want to have small bills ($1- $20 increments) on hand for souvenirs, restaurants, spa treatments, etc., as credit card processing is not always available. US Dollars are commonly accepted in Costa Rica. You may wish to exchange a portion of your money to colones (Costa Rican currency) at your local bank or the airport in San Jose for small purchases such as fast food. You will want to spend this money while in Costa Rica as there is a steep exchange rate to convert back to the US dollar.