Cool thread. I like the idea of using your brain and whatever one may find laying around. There may come a time when you are separated from your usual gear. So this is a good exercise.

When ever I go fly fishing I find tons of line and flies in the trees from others casting errors. I usually find this while looking for my own errant fly stuck in a bush.

I always see cans, buckets, plastic bottles and glass bottles when in the woods. Sad but true and useful in a pinch.

On many occasion at a local climbing crag that is used at night by kids to party at I have found very serviceable lighters and matches.

Thats just a few examples but if you factor in what trash is lying around here in Oakland the possibilities are endless.
Bill