You can always change them at the bank. We usually bring some for larger purchases like housing or plane fare. Oh by the way, if anyone is traveling to Guatemala, US currency has a better exchange rate there than BZ.
The Chinese merchants use big bills to smuggle money out. They often seek them at such times. Most travelers these days carry little cash and pick it up at ATMs as they go with a debit card. Even CC residents who have income back in the States bring their money down this way. Much safer.
AND be sure and notify your card company when you are going to travel. If they are worth there salt they will throw up flags otherwise. It cost me some expensive phone calls when I went to Chetumal without telling them.