what's safe to eat?

I think eating at least a couple of fresh fruits besides yogurt (I don't know whether Mexican food contains lots of vegetables or not as Chinese food does, to provide enough fibers) can help maintain digestive comfort, especially when you're travelling and might not drink normal amount of water per day. :)

I hope fruits & yogurt in the markets wouldn't be too expensive down there. :)

Most Mexican food doesn't contain a lot of vegetables like Chinese food does and the concept of a balanced meal ( like a meat and three vegetables) doesn't seem to exist. The main source of fiber is tortillas, in addition to lots of fresh fruit. Yogurt is widely available at supermarkets and convenience stores. I agree with previous comments about tamales being a safe alternative, if they're not too spicy. The blandness and bulk of the masa seem to calm the stomach.

Lots of great advice here. Thanks to everyone for posting these comments.

I do not recommend eating seafood cocktails from street vendors, especially raw oysters, just about .anywhere.
We now eat lettuce and tomatoes in restaurants that we are confident in. Last week, I hada delicious ceviche-like salad called "tiritas" at Mariscos La Güera, in Pátzcuaro. Also consuming ice in our drinks sometimes; so far without any ill effects, although I HAVE seen blocks of ice waiting on the sidewalk outside some restaurants. (NOT at La Güera. There, the kitchen help robes up as for surgery, complete with surgical masks.)

Wow, thanks for all the input. This is really informative. It also makes me feel less paranoid! I don't want to spend the trip worrying about what I eat...so it's very useful to have all these tips.

I just got back from Tulum. The great thing in Tulum is, there is very little infrastructure so NO ONE drinks the water there. Therefore, all your produce will be washed in bottled water and you're pretty much safe with everything. I had amazing ceviche for $4 (a HUGE plate) at Don Cafeto.

Being that limes accompany almost every dish I think it is a good idea to use them.I heard once eating them will help prevent illness, and they are delicious.Dont know if they work but they sure are good

I don't think you need to be paranoid---just careful. My only comment is that the busiest stands where locals eat are most likely popular because they have the best food at the best price. I'm not sure you can make a direct correlation between popularity and low incidences of bacterial caused illness.

Like I said, everybody (#16) has a theory of what works.
My wife believes that daily intake of a good quality tequila is beneficial, particularly around 5pm.
Who am I to argue?

We talk about this topic frequently - and few people share similar experiences and/or "problems." Some people seem perpetually immune and others are bothered.

I've been traveling in Mexico for many years now and though I don't often get sick during these trips it does happen from time-to-time; I contracted Hepatitis A when I lived/worked in Mexico and on another occasion I picked up a "bug" of some sort that took about 6 months to eliminate after I returned to the USA.

Given the many factors which may contribute to various forms of travelers illnesses in Mexico, I don't think there's much one can do to avoid the risks - short of checking-into an isolation ward. For most of us, the short-term discomfort we experience in these instances is not serious - it passes quickly. However, for some travelers - the risks can be serious, even life-threatening.

My sense is that a doctor probably does a disservice and offers generally recommended-against advice when suggesting travelers take Ciprofloxacin as a preemptive measure to ward off sickness - when a traveler has no other health concerns that warrant such a regimen. I know of people who down many Pepto-Bismol tablets, too, while in Mexico - believing doing so will somehow immunize them (or otherwise prevent) stomach/intestinal problems; I wonder how these people can taste what they eat and drink, given the quantity of the Pepto-Bismol they ingest.

As has been recommended by others in this discussion, I take what I think are reasonable precautions to prevent illness. However, I don't do so extremely - to the level where such precautions interfere with my enjoyment/trip. If I were that concerned, or had health problems about which I should be especially concerned - I wouldn't travel in the manner I do in Mexico. When I have a "problem" I address it then, and there.