Here is a short video of Doug Marcaida (of "Forged in Fire" fame) talking about weapons of opportunity. In this particular video, he talks about using a baseball cap as a weapon!
So, I came across this video of a guy who crafts a katana type sword out of an old leaf spring. It may not be perfect, but it's good to know how to do, you know ... for all your post-apocalyptic needs!