Was about to say belt
whipping with the buckle will bust someones face right open.
But I have a nice heavy 6" piece of steel attached to my keyring, bout as big around as my middle finger, on a nifty keyring that pulls off from the rest of my keys. Makes a great fist pack, the ends both stick about 1" past my hands to knocking pressure points, or holding it by the end makes it like a small club that would easily break skin, esp over the eyes giving a definate advantage. It also works great as a bottle opener if a lighter or real bottle opener isnt available. Or you can open beers if you are wearing a ring......