What About Eating and Staying Well?
Most people know the caveats about drinking the water in Third World countries, but in Belize municipalities, you really can drink the tap water. Having safe tap water probably translates into less food borne illness in general there.
I have had my share of this type of illness, and I have come to the conclusion that the best way to stay well is to mostly eat in restaurants that rely on repeat customers. These are the ones that have a lot of customers for the main meal of the day, lunch from around 2-4 PM. Keep an eye out, because a good one will not necessarily be busy if you want to eat at around 5-6 PM.
This does not necessarily mean that you should only eat where locals do. A good example of a safe one catering to tourists is Restaurant Vallescondido, where all the Yaxchilán and Bonampák tours in Chiapas stop at for breakfast. Another is Comedor Imperio Maya at Tikal.
Getting a Hepatitis A vaccination is a good idea, because you don't necessarily need to eat food in a Third World country to get it and it gives long term protection. As a good backup plan, buy some Cipro (ciprofloxacina) at the local pharmacy when you arrive and have some Imodium along. See travmed.com for more specificadvice.