Either the Gerber STL 2.0 or STL 2.5

The thinnest I've seen is the Ultimate Pen Knife or the 3.0 Titanium Lockback Folder from A.G. Russell

In my kits, I currently have the Mk5 fixed blade but before that I used a Leatherman Squirt and before that the Micra. Although the 1.5" blade is not as useful as a Spyderco Ladybug, the other mini tools (pliers or scissors) are quite useful. I still keep one in my jacket (fastened to the inside of the pocket with a fabric loop). It comes with me on every camping trip as an alternative to the larger Wave.

I am suprised at how many seem to be depending on a folding knife as their primary knife for survival.

I have lots of knives, a bunch are folders but I don't consider any of them as a primary survial knife. I consider a folding knife as one that is already broken in the middle, it has a built in critical weakness.

I carry a SAK Farmer as a pocket knife, always but I also have a fixed blade, with a full or nearly full tang with me on all wilderness trips.

I think the take away from this thread is that in real life (as opposed to Rambo movies) a folder is perfectly adequate. I have found that fire lighting equipment has been critical on several occasions, that there have been times (mostly in the past, pre-LED) when i wished I had a dependable light, but I can not recall ever muttering, "I wish I had a bigger, heavier, longer fixed blade knife." I do have some in my collection, but they are rarely carried. They do have their uses, but, let's face it, they are very specialized.

I have found a machete useful on trips to Mexico, but that actually was not in a true wilderness setting.

I'm with you. In a survival situation if I need to chop or pry, a folder will fail. I realize that there is only a small chance that would ever happen, but that's the case with 90% of the subjects we discuss here. I carry a small folder or Leatherman and a larger full tang knife when I go into the forest.

I usually carry a fixed blade when I'm hiking, but the rest of the time I carry a folder.

Given the time and the materials, my hope is that I could use a folder to make a good prying tool. A good chopping tool is tougher -- I've never learned flint knapping and it doesn't seem like a good use of my limited training time and budget.

Here is Flint Knapping 101. Take Rock A and smash it into Rock B (or anything else that is hard and unyielding). When the dust settles, pick up the sharp pieces and use until dull. Repeat as necessary.

That is basically how tools were made for thousands of years, and this while this technique is a far cry from the beautifully crafted Clovis points and Solutrean blades which are at the apex of this technology, it will work in a pinch. If you don't have flint or chert handy, don't despair. Glass works better than almost any natural product, even better than obsidian.

I don't mean to imply that one needs to carry a Rambo sized knife in the woods. I carry a blade between 3 1/2 and 4 1/2 inches. My daypack has a Mora 510 in it and I have used that for awhile now.

A blade made from a rock may be useful for some knife work but to use it for long will be mighty uncomfortable on the hand. My Mora 510 and sheath weighs less than 3 ounces, less than a Spydeco Tenacious.

In a tin - SAK (one with a saw for my preference) or a small Spyderco - the Grasshopper slippie is a good one.

Bear in mind weight as well - I love the Boker Subcom, but it is very heavy for a small knife

As ever, these are all points on a spectrum - given the choice, a full sized axe, saw, knife and multitool etc would be with me in a crisis. However, as others have said, it's only useful if you have it when you need it

I think the Victorinox Farmer is poorly named as it connotes an image, that unless you look up the blade configuration, doesn't do it justice

aluminum alox handles with lanyard ring
only 3 layers
main blade
excellent saw
can opener w/small straight blade screwdriver
cap lifter w/large straight blade screwdriver and wire stripper
awl that opens on end that you can actually use