I keep the small sized book in all of my kits. I find the information would help me more in a longterm situation rather than a short term. I would say a situation that lasted more than three days would be where I pulled out the book.

I would use the book more for ideas that I hadn't tried before. For instance in a survival situation I might be inclined to make snares to catch food. If it came to that then that would mean I had all the time in the world to research different traps that I never tried before.

In the short term most of the skills I would use are skills I have practised over and over again to memory. However if I am trapped on a deserted island for the rest of my life, then the book is well worth the weight and that is why I carry one in each kit. That and for the fact that for my personal motivation I find reading to helpo me cope with stress. So the book is more of a personal religous item for me than anything else.

Knowledge wise I think your better off with the Air Force survival manual, but its too heavy and bulky for a survival kit you carry all the time.