While it is definitely the house-made hot foods and the in-house bakery that sets this place apart (be sure to try the Tortillas, made fresh all day, and kept on trays atop the "to go" food case, not with the other tortillas) I think you will find that Supemercado Morelia has produce items from Michoacán that you will not find elsewhere. As to the canned and frozen items, they mostly represent the lines of the Major Mexican distributors (Goya, La Preferida etc.). However, mixed among the old standards (which are reasonably priced), there are foods that are peculiar to the Michoacán region such as frozen Mamey fruit (which they also often have fresh). They also have a good selection of Mexican Beverages. While there are other alternatives for canned Mexican goods in the area, Morelia does a great job of keeping their shelves neatly stocked. When a can is removed from the shelves, within minutes an employee moves the other cans forward to fill the hole. When you couple the pride of ownership with the excellent bakery, flawless produce, unique prepared foods and line of in-house made condiments, the place cannot be beat. It seems the inventory is not as great as other larger Markets, but I have never not found what I was looking for. They may just have fewer duplicate items on the shelves.
A good place for a huge array of Mexican spices and items like bunches of Fresh Thyme (sold at the registers), the Rogers Park Fruit Market is a must go to. Besides Mexican spices and condiments, they have a massive selection of Caribbean foods and sauces. They must have 40 different types of Jerk-Sauce.