Crank Bros Multi-17 Tool

I keep this tool in my bag all the time, its great! Compact, lightweight, and has all the tools needed for a road side repair. Ive fixed broken chains, used it to true a wheel so I could get home after a spoke broke, and fixed a slipping seat post. I felt a lot safer venturing a long ways from cell phone service after I got this tool.

If you only want to have a single tool in your bag or jersey pocket, this should be it. Solid construction and with a layout that allows you to really torque allens, screws, etc. and not feel like you're going to break the tool. The rubber belt that surrounds it to help keep the tools from popping open is a bit tough to deal with, but otherwise it's a fantastic tool and I highly recommend it. If I'm in my workshop tinkering on my bikes I'll often find myself pulling this out of one of my bike's seat bags to do minor adjustments, even though I have a full set of allen wrenches nearby.

I think this tool is unparalleled by its competitors. For it's impressive thoroughness, it's unbelievably compact and minimally modular. It's got an 8mm hex for your pedal spindle a variety of spoke wrenches one of which makes an excellent valve tool and need I say more? an uncompromising chain tool! There's very little that could go mechanically wrong on a ride that this guy is unprepared for. If you have a friend that also hasn't got one yet... buy two!