I've been in the military for over ten years, and I leave the country 4-5 times every year on military trips. It just so happens that I'm going to South America on Wednesday. We received a medical briefing on Latin/South America as part of our pre-deployment briefing. They told us:
-Don't drink the water.
-Drink only bottled water
-Eat only food that has been cooked or boiled
-Bring medicine for diarrhea
-Tell your bank you're leaving the country so they don't block your cards
-Watch out for pick-pockets
-Your cell phone may work outside the country (call your carrier for details)
-Don't stand out
I know this isn't a very positive list, but keep in mind it's coming from a military perspective.