I recently ran across the site of a gentleman by the name of Paul Elkins who builds bikes, shelters and all kinds of strange things. Here is a link to a video he made on an improvised homeless shelter. He made it out of four, 4 X 8 sheets of coroplastic (also known as coroplast) and cable ties. http://bit.ly/rZ5II4 It looks like a very interesting idea and can be built very cheaply. He says for less than $100. There are plans on his website. Coroplastic is available in many different colors and is often used by sign shops.
On his website he has several other useful ideas, including taking one of the old bobbins from your wife sewing machine and using it to carry fishing line in a small survival kit. The hole in the center of the bobbin will hold two split shot.
His website is http://www.highmileagetrikes.blogspot.com/ . You kind of have to hunt a little to find the good stuff, but it is there.