I carry a Crank Bros M17 multitool with a chain breaker. In the last 4 or so years it's twice saved me from being stranded out in the country 10+ miles from home. First time was when I reused a Shimano chain pin which you aren't supposed to do. It came apart on a ride but luckily I had a spare pin in my saddle bag and fixed it. The second time was when I was riding an '80's Schwinn LeTour I had just restored. The old freewheel locked up for a split second, threw the chain off and it actually ripped my RD right off and twisted the hanger beyond repair. I was able to set it up as a single speed to get home (then had to throw the frame away).
If you carry Co2 this bracket is nice to have. You can find them on amazon.
