Funny, I keep everything I've ever bought in terms of field guides and hiking books on the bookshelf gathering dust mostly, especially the ones I haven't gone ahead and learned first hand, like knots (lousy at knots except for 3) and mushrooms. Which makes them less than useful if the SHTF, and I'm now dependent on finding edible mushrooms - a field guide will only lower my chances of poisoning.

If I'm asked to tie a Double Splayed Loop in a Bight or a Double Fishermen's Bend to save our lives I'll admit defeat for lack of being that prepared, there's no time to look at a book then; a prussik, bowline or square knot have mostly worked for me.

I always pack Buck Tilton's Backcountry First Aid in my FAK, and will read it on the trail in idle hours. I'd rather have that one with me than sitting at home, in case the WFA training fails me or something really weird happens, and I want to quickly consult, or have non-WFA trained people quickly consult before treating me!