I've been thinking about this one and having a hell of a time coming up with something- but I've had a few ideas. Unfortunately they are all in the "something phase"...
Something that would break fairly easily into a sharp edge.
Something that is attached to a piece of light gauge rope/cord that could be swung.
Something with a point- i.e. a metal pen casing. Hell, even a bic pen is slightly better than my bare hands.
A roll of quarters makes for a hell of a punch, but almost certainly breaks a bone in your hand.