We have no ATMs in Placencia that will accept international credit cards. (At least not yet, although two are promised, 1 by Scotia Bank, 1 by Atlantic Bank - not Belize Bank here.)
If you plan to use credit cards, bring a Visa. About 3 months ago, MasterCard imposed a $0 floor limit on ALL Belize businesses. Therefore, smaller businesses that don't have electronic credit card machines will NOT accept MasterCards after business hours (they can't call and get an authorization code).
Traveler's checks are fine, but PLEASE, don't fill in the name of the merchant or the date! If you do, the merchant will have to deposit the traveler's check in the bank, and the banks hold them for 40 days before actually depositing the money in the merchant's account. If you leave the date and payee blank, the traveler's checks can be used as cash.
You might want to check out our Dis 'N Dat page for more info about Placencia, its banks, tours, food, customs, etc.
http://www.destinationsbelize.com/dis_n_da.htm Have fun!
Mary
Destinations Belize