My LBS told me not to bring a chain tool on my tour because "I probably won't need it." I looked up how chain tools work and realized I would have had a nightmarish time trying to repair a broken chain without a chain tool. I bought the Topeak Hexus II.

Another bike shop on the way put a 10sp chain on my 9sp bike, which resulted in my chain flying off four hours later (and, consequently, a train ride across Boston later). I had been in cadence when it flew off, so I jammed it in my crank and bent a link. My chainbreaker worked to make the chain useable within 10 minutes. Accidents can happen anytime. Andrew Skurka, the long-distance backpacking guru of the 21st century, has two categories: Ultralight and Stupid Light. I will never travel stupid light.

Anecdotes:

I've never met a Local Bike Shop that I completely trust.

I don't trust the tire levers on the Topeak Hexus II either...