Avoid food processed by street vendors. Don't drink beverages with ice cubes. Avoid dairy products unless you know they have been pasteurized. Don't share needles with anyone better yet, don't use illegal drugs. Don't swim in fresh water.
Salt water is usually safer.
Iodine tablets and water filters to purify water if bottled water is not available. Your prescription medications. Insect repellants, sun blocks. This is not a complete list of what to avoid and what to do. Ask your doctor to check for the specific area you will be traveling.