If you live anywhere north of the 30th parallel, and spend anytime in the bush, buy this book. It's as simple as that. The amount of knowledge Kochanski packs into this small, easy to carry package is insane. Shelters, firecraft, axecraft, hunting, foraging, trapping, fishing, you name it, and I bet it's in there. As mentioned, it relevance dips the further south you get, as he mainly lived in the Canadian north. But, even if you aren't in boreal forest, a lot of his craft can still be applied in other environments.
On a sidenote, if you're an outdoorsman, as well as an active soldier, DEFINITELY read this book. You couldn't ask for a more comprehensive, and easy way to add to your repertoire of soldiering skills, and will probably take more away from it then you would in most military-ran courses on the subject.