@boomerang,
Sayer here!
Yeah, I agree with the Cheez Curlz bit. I tend to not have junk food cravings UNLESS I diet -- which is another part of why I avoid dieting. (I eat fine if not perfectly if I'm not thinking too much about what I eat, but if I put something on the verboten list, THEN I want it.)
I'm trying to remember specific examples. I wanted iron-rich foods when I was a teenager and turned out to be anemic. (I wanted the foods before I knew about the anemia.) I've had major tuna fish cravings after exercise -- just plain tuna fish. I've found out since that tuna is a really good post-exercise food (salt, protein, fish oils that do good stuff). Hmm, that's all I can think of now specifically, but I know I've had these lightbulb moments a lot. Oh, when I was pregnant, too -- not just cravings but aversions. They all made sense once I investigated them.