Be advised, though, that vitamin D is one of the ones that can be toxic if you get too much in you.
I find the whole "field expedient insect repellents" area to be one of the most critical for outdoorsmen / wilderness-survival-interested people. West Nile virus and St. Louis encephalitis have both made their presence known where I live, and one result is that I've been vastly less inclined to let my kids sleep outdoors without a mosquito screen of some kind. It's one thing to build a lean-to that'll keep out most of the rain; but building something that will keep the mosquitoes out is a more difficult proposition. It may be coming to the point where we're going to need mosquito netting--and I mean a LOT of it--as a standard feature in survival kits. I would not be AT ALL surprised to see a resurgence of malaria and yellow fever in the U.S. (we used to have epidemics of these diseases), now that anti-malarial drugs are beginning to lose their effectiveness, the country is forgetting that people used to drain swamps and take steps to keep the ground dry for a reason (I see lots of public-construction projects that are engineered so as to keep large amounts of standing water--obviously lessons of past epidemics are being forgotten); and increased travel between tropical countries with malaria problems and first-world countries is likely to mean that there may be more malaria-bearing mosquitoes flying around than we're used to.