I think you're on the right track. A sawzall-type blade, with a few tweaks, is a "cut anything" tool. Not fast, but effective.

From my experiments, I'd suggest:

- Go with a bi-metal, fine-tooth blade (usually 14 tpi IIRC) at least 6" or longer. It takes a lot of power to use a coarser-toothed blade by hand, especially without a handle.

- My preference is to grind both ends of the blade to a quarter-moon shape, all edges carefully smoothed so I can use it as a pull-cut or push-cut. You never know which you'll need. Also, rounded ends mean nobody except airport security gives them a second glance.

- Another option: drill a couple of holes in the blade so you can mount a short handle if needed.

I would even hand these out to people who knocked on my door asking for help. Useful as a tool, useless as a weapon. Perfect.