I find that the text for a WFA course I took is what I have referred to most often. It's from the Wilderness Medicine Institute, which is part of the National Outdoor Leadership School (NOLS).

I have an older version, but, the current one is available at:

http://www.nols.edu/store/product.php?productid=16455&cat=267&page=1

Of course, I'd have to say that it was the course, not the book, that's the most valuable. Spending a weekend in the woods with a bunch of folks, practicing, dealing with scenarios, improvising, great stuff.