The Belize Dollar has a fixed rate of $2BZ = $1US. US currency is accepted everywhere.

There is no need to change US currency in to Belize dollars when you arrive in the country.

Generally speaking, it is wise to bring as much cash as you anticipate you might need, and then use your credit card for cash withdrawals. Remember you will get Belize dollars from the ATM.

Banks charge a fee to convert travelers checks and most restaurants, resorts, and shops seem reluctant to accept them now.  

Credit and debit cards can be used in most stores, tourist facilities and larger restaurants. Grocery stores are usually cash only. 

There are 3 ATMs in Placencia

Be sure that you call your credit/debit card issuer and let them know the dates you will be traveling internationally. This avoids the hassle of your card being declined unexpectedly.