How Much Cash Should I Carry?
The amount of cash you should carry depends on what you plan to do. If you envision a day of eating at better restaurants and buying souvenirs, you’ll want $75-150 per person. However, if you'll be eating brakfast at your hotel and don't plan on doing much, $50-75 should be sufficient.
Dollars can be used at most places, although in smaller restaurants and when hiring local transportation (like tuk tuks) you'll want to use quetzales. Having small bills is always helpful.