I've written extensively about the food I ate on the Appalachian Trail. Some people have asked about vitamins and supplements. The answer is, yes, I did take vitamins while on the trail. Although I did my best to eat a healthy and nutritious diet, the reality is that there isn't a lot of non-perishable, calorie dense fresh food options. Also, the demands being placed on me physically and mentally are over and above the norm.
For reference, I am not a big supplement taker. In daily life I use 3 supplements that are doctor directed to treat my personal medical problems. Those are Floravital to treat anemia, Vitamin D, and Vitamin B complex (for deficiencies in both). I also take fish oil or Flora's 7 Sources for additional Omega-3's during periods of high intensity training.
All supplementation should be considered with your health care professional.
For those that are curious, here are the supplements that I found to be critical to maintaining health on the AT (and the PCT). I chose these specific brands because I trust them to be of high quality. It's important to realize that the supplement industry is not regulated by the FDA and therefore a company can put anything they want into them. This is why it is so important to do your research and discuss your plans with a knowledgeable professional.