Re: Carbonfiberboy--"While I use various nutritional supplements at home, I don't use them when touring. PITA. I think the extra food required when biking almost every day provides more than adequate nutrition. I'll vary my touring diet to suit how I'm feeling and that's about it."

While your premise is mostly true when not touring in remote areas or areas where "healthy" options don't appear to be available. It is much more difficult to eat healthfully when touring in third world countries. Of course, I don't think the OP was thinking of international touring.

In many areas in the United States, a convenience store is the only source for purchasing "food" (there really isn't much "real" food in convenience stores). I certainly do the best I can with what resources are available, but many times when touring my daily food supply is a compromise, at best, compared with the food choices I make at home. I find that a few well chosen supplements are very helpful to fill the gaps when touring.