To eat, or not to eat, street food, that is the question.
I'm familiar with the advice to avoid street food in third world countries, but I don't follow it. Instead, I have my own guidelines.
1. Don't be stupid: Look at the stall, the vendor, the food. Does it look right? Is the stall clean? Is the vendor presentable? Is the food hot/cold like it should be? Is there an unpleasant aroma? Just because you're considering street food doesn't mean you should volunteer to be a victim. If the food doesn't pass any one of these tests, give it a pass. There are more, I guarantee you, there are more. I think food hot off the grill is usually pretty safe, as long as things look reasonably clean.
2. Look outside places locals congregate: For example, just outside the local market near me here in Manila there are a wide array of vendors selling both fresh fruit and vegetables and prepared items. I'm leery of the fresh fruit, but sometimes Mexica buys some and it's better than in the stores, mangoes for example are generally more fresh and tasty at the street vendors, and cheaper.
3. What do the locals eat? They'll guide you, even if you're alone. Some stalls are more popular than others, and look closely at the more popular ones.
4. Do you recognize the food? If you recognize it, go back to step one, does it look right, smell right?
5. Easy does it: Don't feel like you have to buy the whole cart. Buy their smallest offering and give it a try. The great things about street food include a reasonable price, which usually means small servings, so you can afford (financially and physically) to just give it a try. Even if the food ends up seeming unpleasant to you, you haven't really lost much.
6. If you have a local guide, take their advice and let them do the purchase. Of course, this only makes sense as far as getting the right food, but you also protect yourself from being overcharged, There are no price signs on most of the carts here, so you have to know the price, and I don't.
Examples from the Philippines of street food I have really enjoyed include roasted peanuts (a real favorite), grilled bananas, grilled sweet potatoes, shawarma (the Arabian version of a gyro), and various grilled meat--chicken and pork skewers. I've avoided the grilled chicken intestines and the balut (fertilized duck egg, boiled and eaten in the shell). I've never been sick after eating street food (knock on wood).
