Beware! Both credit cards and debit cards have been jacking up their international exchange fees like crazy. Even most debit cards now get hit with several percent international exchange fee, plus usually a buck or two by the Belize bank and maybe another few bucks from your home bank for using another bank's ATM.
For example, my Wells Fargo debit card now charges 3% on all foreign transactions, including from ATMs and for foreign purchases. That's not including any foreign ATM fees.
Citibank debit cards charge you a 3% international transaction fee, plus $1.50 ATM fee if it's not a Citi branch, plus whatever fee the local bank charges (usually BZ$2-3). Bank of America charges 3 to 8%, depending on whether or not the merchant imposes a "Dynamic Currency Conversion" (DCC) fee. Amex charges just 2%, but in Belize the conversion rate from Belize dollars is a little less than 2 to 1.
Usually credit and debit cards give you the best available currency exchange rate, but that's not true in Belize.
Altogether the fees can add up to 5%-6% or more of the money you get. And you may not realize it until you get back home and check your bank statement. And that doesn't include any interest charges you may incur on a credit card.
Some U.S. cards now charge an international exchange fee even if the charge is in U.S. dollars and there's no foreign currency exchange involved, as long as the transaction took place outside the U.S.
Best to check with your bank or credit card issuer to see what the fees will amount to. With all these fees, it may make sense for some travelers to go back to the old traveler's checks, especially if they get them issued free. However, some businesses will give a bit less than 2 to 1 for TCs.