This was a huge discussion in the past. Most grocery store items do not have the protein needed for an adequate substitution. However, many people have used the South Beach bars in place of the MF bars (last I heard it was SB cereal bars). Those posts used to be pulled off the MyMF boards almost as fast as they went up.
What many people have done is to buy from other meal replacement plans like dietdirect, mydietshopz, Lindora, New Lifestyle Diet. They all sell the same meal replacements under different names. Dietdirect & mydietshopz also sell from other vendors.
They are a different option & have a diet program slightly different than MFs 5&1. All include the meal replacement packets & a healthy meal. The items aren't totally interchangeable w/MF as the carbs/fiber are lower. (You could add FiberSure to take care of that if you wanted.) Some items like some of the bars, soups, & hot drinks are high protein snacks & not meal replacements Many people prefer their shakes as they are based on milk protein & not soy protein. The taste is far superior. The cost is much less than MF.
It is a personal choice what diet plan one wants to follow. I'm not plugging products from any particular plan, just providing some information. How everyone choses to lose weight is their own personal business. And as long as it's done in a healthy way that is what should be important.