Chopsticks have already been mentioned, but most would break very easily. I have a set made out of Titanium that would double as a weapon very nicely.
I also have a PDA stylus made out of Titanium. Has a nice sharp point.
I always wear steel toed boots, which could be useful, and I also carry a Surefire flashlight, which could be used as an impact device or a fistpack. Frequently, I wear a "riggers" belt that has a very large steel buckle that would work well when swung.
Change or large batteries in a sock is a great, discreet idea, but its really only useful on an airplane, where no one would think anything of batteries and socks in a carry-on bag.
However, in my house, I'd grab my katana or bowie.
