A FiberFix kevlar spoke can be used to replace a broken cassette-side spoke without having to remove the cassette.
I carry a patch kit and two or three tubes. I've gone through two spares before and then had another puncture. Really glad I had the patch kit.
Also, I usually carry CO2 and a Road Morph pump. I use the pump at all times, but either a) the pump could fail/break/whatever, or b) it could be freezing rain and I could be just too exhausted to deal with a pump.
...possibly too many redundant systems, but the extra weight (1 CO2 and a patch kit) is minimal and I like having the backup.
Dan