What to Eat
When traveling it is so easy to spend money unnecessarily. You don't have to plan too far ahead either to be smart. In Mexico realize that most people shop at second hand stores and little tiny places that are away from the main parts of town. The more you go into small rural areas the more likely you are to being able to get prices much closer to what a Mexican citizen might pay.
Instead of shopping at Walmart or even Calimax for that matter you should go to the small swap meets. There are almost always people there selling fruits, veggies, honey, and most of it is organic too.