I was going to stay out of this thread, but as qtla9111 said, "I don't care for these threads as it spreads some old myths as well as misinformation about Mexico and scares off possible Mexophiles."
Like Mexicowanderer, navagator, and qtla9111 we live in Mexico full time. We have a decent feel for what food is safe and what isn't, at least in general. We all have opinions on it, some strong like mine.
We believe that most tourists who get the touristas are suffering from too much sun, too much tequila, too much hot salsa and too much fun. If that isn't it, drink a lot of fluids, use Pepto Bismol and/or Imodium.
We don't have a Costco here, but do have a Sam's Club. We are members for one thing: Dog food. They have a quality dog food that our dogs do well on, our other choice would be imports. Considering how much our two weimaraners eat, the membership is worth it. We have two supermarkets, and shop at one weekly when the maid and gardener are here. That is basically for the stuff we don't want to have to hunt for-pasta, toilet paper, basics. Everything else pretty much comes from the mercado, beach or street corners.
I'll go down Mexicowanderer's list. If you watch those vendors with fruits that offer you a sample on the end of a knife, they aren't handling the edible portions with their bare hands, because of cleanliness. Watch the taco vendors-if they handle food they don't handle money-or if they do, they put their hand in a plastic bag to prevent contact with the dirty money. Watch McDonalds. They handle food and money.
That mayonnaise? Commercial mayonnaise is shelf stable, even after opening. Refrigeration is only suggested to maintain quality.
Eggs in Mexico, and in most of the world except the US are unwashed which makes them shelf stable for a long time. Cracked? Really want to take a chance in any country? Occasionally I'll hard boil cracked ones for the dogs if there has been an egg accident.
RV refrigerators aren't the most efficient, so hopefully people keep a thermometer in them and check it. We found that adding a small computer fan to the outside coils and one of the battery operated fans to the inside makes a HUGE difference.
Here's the biggie, and it's true. Unless there is visible dirt, we don't wash our veggies and lettuce. Honest. US or Mexico, nope. Cook it and eat it, use the lettuces, cilantro, onions, and other great goodies we buy from the ladies behind the market. Our personal choice.
Shrimp is one of our favorites. In Mazatlan, we always bought from the shrimp ladies on their street, they are in washtubs with water and ice. Yesterday we bought a kilo of locally caught shrimp from our fish guy who sells on a corner with an ice chest, steamed them and had a fabulous lunch. Obviously, look and smell what you are buying. We have seen very nasty shrimp in major chain stores in California, but not here.
The meat market!!! We love buying meat that smells like meat, not a plastic package. We don't buy meat in the grocery store. Our favorite butcher has a refrigerated case and a chest freezer, but he does hang his cecina to air dry. He has better filet mignon that we can get in the US, then there are his ribs, carne enchilado, liver, heart, I'm drooling! The guy next to him does pork, and it's just as great. We think when you eat meat you should be aware that you are eating an animal, and appreciate it. We don't soak our meat, we usually marinate it but that's for flavor.
Ranch cheese? Sure, we buy it, but from a cart that appears regularly, someone with a table in the market, not a random person.
OK, chicken. Zihuatanejo has the most amazing chicken anywhere! We finally figured it out. It's sold in LOADS of little tiny places. A block of ice covered with a cloth, a person with a stick with tassels waving it over half a dozen dead chickens, gutted and plucked. They will cut you any pieces, filet and pound a breast, whatever you want. The livers are fabulous, so different tasting. When you get it in your hands, you realize it's not really cold. These are extremely fresh dead birds. The abattoir is in the center of the block with little tiny openings all around. The people are literally getting freshly butchered birds and selling them a few at a time. It's amazing in flavor and texture. It doesn't compare to any other chicken. Yes, as soon as we get it home, we refrigerate it, and we shop with an insulated bag with a frozen bottle in it.
Where do we eat? Wherever it looks good, smells good and there are other people. Does this include street food? Yes. We probably have 4 meals out a week, generally breakfast, and two of those meals tacos of various types another quesadillas, I'm hungry!!
When we lived in the US we found that we would have "intestinal upsets" occasionally from eating fast food. Here, we may have a meal that sits heavy, but considering how often we grab food out, we feel food handling practices are very good.
So, what does this all mean?? Come to Mexico, have a great time, eat strange things, do fun things, enjoy our country.