I actually use a tarptent, or a remaindered 9x9 REI tarp that cost me $24.93, but a friend likes the Kelty Noah tarp of the same size, currently ~$60. Its sturdy, and has grommets and tie out lines built in, and can set up to keep a bunch of us out of the rain at camp time. Very versatile, and not as pricey as silnylon, but not as light either. I say any port in a storm, I have several tents set by for emergency shelter, but as long as the grommets are sturdy I keep a couple general purpose tarps and some paracord in my emergency supplies. If not for me for my neighbor.

The silnylon tarps are fantastic with good strength-to-weight ratio and they pack compactly. There is a lot of info on them on the web. The ultralight backpackers love them. The Hennessey Hammock folks sell a hex silnylon rainfly that can serve as a deluxe stand-alone tarp. It has sewn-in pockets at each corner that hold a length of lightweight cord. It came with my hammock; I doubt I would pay the $129 price by itself. But it now goes in my pack on all day trips as an emergency shelter.

Steve

Also included in this group are clothing and versatile, fire retardant and warm-when-wet wool blankets for people living in a place where it gets cold.