No need to change your US money to Belizean as US dollars are preferred and spend just as well. The exchange rate is fixed at two dollars Belize equal 1 US. Usually you'll get Belizean change. Don't worry, you can spend what Belizean change you have left at the airport buying rum, souvenirs, etc. Also most places post their prices and note if they are US or Belizean. If in question, ask