Those look like T-style jig saw blades.

LOL. before this thread came up I pretty much said what I had to say in the "Ravenlore's Possible Bag" thread:

Also, I have looked at the Gerber with its ability to use small saw blades. IMO those saw blades are much too small to do much real work. Unlike a knife, where a small one can do big work, a saw depends on length to get a good number of teeth across the work. A electrically powered jigsaw can move the tiny blades back and forth a thousand times a minute and get the job done quickly. Using such small blades by hand is pretty miserable about the time you get the blade moving you have to stop and reverse direction.

Even under ideal conditions a 4" saw blade is about the smallest saw blade I consider to be practical to use by hand. The saw blades on my Leatherman are about 2-1/2" and only good at a last resort. Even a 4" blade is pretty much short-stroking it and you end up working mighty hard to get anything done.

Anyone doubting this should try using one of a jigsaw blade to cut through something light, like a softwood 1 by 3 or #3 rebar. These are pretty much the minimum capability in my book. If you can't saw through these in a reasonable amount of time your better off reconsidering your options. A tiny blade will see your arm tired before the job is done. And don't be in a rush.

An 8" or 12" blade is much more useful if your intent is to get something done rapidly.

No matter which saw you use or what your sawing it pays to lubricate the blade with some wax to make it sawing easier. Makes a big difference. Beeswax is perhaps best but a wax candle, perhaps from your fire starting kit, will work.
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I have carried a 'Wood-Zig' pruning saw or a demountable 'Sven saw' if I have reason to believe that I may need a wood saw. One of these bow saws will take any standard 12" hacksaw blade. These blades are kept under tension and are more effective than any 'stab-saw' type blades because they are thinner and are kept straight by being under tension. The only weakness is you need to be able to span what you cut so, unless your really creative and determined, you can't use it in a blind-cut situation.

There are several nice aluminum SawsAll blade holders that will allow you to mount any standard reciprocating saw blade in a comfortable handle. Lennox makes a nice one. You will still have a sore arm trying to do what you can do in a minute with a SawsAll but a longer blade, ideally 12", or a type optimized for the material your cutting is far better than short stroking it with a silly 2" long saber saw blade.

A SOG Seal Revolver might be worth considering. It is a knife/saw combo in one blade (not a folder). They also offer an even more versatile model with a gut hook (Hunter model).

http://sogknives.com/store/REV-7.html

Disclaimer: Not affiliated...blah blah blah

Stanley makes a handle for using Sawz-all blades. I've also seen this designed to use 1/4" hex bits. IIRC it was from them too.

Sawzall and reciprocating blades are nice, but they are designed for something doing how many hundreds of RPMs? YOu do how many tens of RPMs? So you are going to have a hard time taking on metal, and the carbide blades will test the patience of a Buddist monk.

If I have to go utterly ultra light, I'd probably go with a bow saw blade packed in a length of old garden hose, and some screws and split rings. Make a handle for it. NOt the best way, but it does work. Or if you have two people, two lengths of P-cord and turn it into a small two man saw.

The Kerskaw blade trader blades are not small 4-inch blades. The blades are almost 9 inches long, (8 inch worth of sharp edge.) The handle (the wood part ) is 5 inches long with another 1.5 inches for the latch part 6.5 inch total handle.

I've found that gripping a saw blade with the pliers in a Leatherman tool to work well. For a while I carried two 3" saw blades (one for wood, one for metal) in an Altoids PSK along with a Leatherman Mini (now discontinued but available on ebay from time-to-time). It made for a very compact package with a lot of capabilities.

This is knife in my BOB and hiking kits. It is 8" closed, 14" open and weighs no more then 10 oz.

I have had the knife for 3-4 years now and has proved itself from the far north of Canada to the Rockies several times. The dual rows of teeth can cut through a hefty size piece of log. If the teeth get a little dull, they can be touched up with a small file. There is also a locking mechanism to keep the blade from doing a number on your fingers...

The original cost of the knife was $14.99, the blade is replaceable at a cost of $3.00 which I just replaced it for the first time a few weeks ago.

+1 !!

I also keep a Gerber fold-up saw handy. Doesn't take up much space, and works well as a pruner or as a bone saw.

I worry about my SAK blades because they don't lock.

I have a "Pocket Chainsaw" in my BOB. It's very similar to the Walmart "motorcycle chain" type in this thread, except instead of the webbing handles, it has small wire looped handles that are designed to have a piece of wood slid thru them to use as a grip/handle.

I just googled it and they do have a website:

http://www.pocketchainsaw.com/

It cuts fairly well for what it is. Packs up in a round tin about the size of a chew can. I'm not sure of the weight but if you're weight conscious about your kit, this thing is fairly heavy for its size.