Although I generally scoff at all the "If you could have only one" threads because I usually regard them as unrealistic, I view this one differently.
I normally carry a heavy-duty fixed-blade (5" blade, almost 1/4" thick, D2 steel), but I don't carry it everywhere I go so I can't always count on having it on my person.
When thinking about a SHTF scenario, I try to think about situations that I might realistically find myself in, and what tools might prove to be most useful in those situations.
I generally regard folders as simple cutting tools, but I can think of a few realistic emergency situations where I might need to use a folder for something other than a simple cutting tool. Like for example- if I were trapped in an elevator (power outage) and I needed to pry the doors open. I live in California, and earthquakes are a concern here (we're still waiting for the BIG ONE), and if I were trapped in an elevator I might be there for days before rescuers came to get me, or longer. In such a situation, my survival might very well depend on my ability to pry the elevator doors open.
Another example is being trapped in a collapsed building (earthquake again), and I might need to chop my way through a wall if I am unable to get to any doors or windows.
If I were faced with either situation, and if the only tool I had to use was a folding knife, I would want a pretty strong one. I'm not up to date with heavy-duty folders, but the Benchmade Adamas looks capable. I've also seen some Zero Tolerance folders that look pretty tough.
Thinking about this subject, I realize that when I'm not carrying my fixed-blade I don't really have anything on me that would make a good prying tool. Since I normally carry my fixed-blade I pretty much take for granted that I have a prying tool with me. But like I said, I don't always carry it. I normally carry adjustable pliers and a 6" adjustable wrench (one attached to each boot, they often come in handy), and I always carry 2 small AA Fenix flashlights (one in pants pocket, the other attached to a boot), but when not carrying my FB I would be screwed if I needed to pry something. I've thought about adding a small prybar to my other daily-carry tools, perhaps that's something I should look into further.
