The "who takes a spare" thread got me thinking about what we carry and why. A lot of it is based on personal experience - we didn't carry something until we discovered we needed it... Basically, we carry:
brake and shifter cables
John has the brifter brake/shifter lever and we don't trust them so carry a bar end shifter to put on if it breaks
I think that's it for spare parts for us. What about you? What do you carry?