IMO the key to successful street grazing is to eat where the locals eat. Nobody, including locals, wants to get sick. And any vendor who gets their customers sick isn't going to be in business very long as word gets around. Look to be sure the vendor keeps the meat and perishables cold, runs a clean stand and thoroughly cooks the food. Wipe off your cans and bottles before drinking beverages or, even better, use a straw ("po-po'-tay"); generally provided by vendors without asking.

Over many years I've eaten in the street in many different countries and have only managed to mess up my intestinal system twice so far. Once in Tokyo and once in Mexico City. In Tokyo I think I got some bad sashimi (unusual, but it can happen) and in Mexico City I drank some Agua Fresca (flavored juice/water over ice) against the advice of my future Mexican in-laws.