I amn normally pretty sensitive to any food bugs around, and I have eaten at most of the fast food vendors in "the Park" with no hint of any ill effects. As to water, though, if you run the tap water through a good filter you may be horrified at what's in there. I started doing that, which is when I switched to bottled water. It's not expensive either - obviously smaller containers cost more per pint than larger ones, but a 5 gallon container costs around US$2:50.
In any climate such as this you should always ensure you have current protection for Hepatitis A & B, but you're probably less at risk here than in most other destinations with similar climate.