Survco Credit Card Axe - $29
There's a lot that the mantra "you never know" makes people carry, but it's a little more reasonable when the gear turns out to be the size of a credit card. Sharp, tiny, and strong, this little stainless-steel thing can easily be lashed to a handle, stick, or bat to cut stuff down. Don't use an axe much? It's also a multitool with 20 other functions.