I have always carried spokes, and broken quite a few. As whittierider mentioned it takes a bunch of heavy tools to remove a cogset, which is necessary to replace a spoke on the drive side of the rear wheel. A video is at http://www.parktool.com/product/cassette-lockring-tool-FR-5
. In the old days it was worse with a wide variety of freewheel removal tools and a not insignificant chance the freewheel would break in the attempt. But in these modern times I carry some kevlar spokes (fiber fix). These may be the best thing ever, since I started carrying them I haven't had a spoke break, yet alone one on the drive side of the rear wheel. They are also work for both sides of the rear wheel and the front wheel, which probably all require different length spokes (so 2 spokes may not cover the 3 lengths you might need.)
I wouldn't carry a chain, but I carry and have used a spare master link that is appropriate for your chain. I would skip the spare quick release. I carry and have used spare bolts when some holding the rack jiggled out and were lost. I have carried a little tube of blue locktite ever since, which may be an over reaction. I definitely use the locktite when installing the rack. Personally I don't carry spare cables, but I would recommend a careful inspection before you leave, especially of the brake cable near the fat end in the levers. Look for broken strands. Also check any cable stops in the brake system, I have had one disintegrate which leads to a total failure of that brake.
Some judgement on what to take is required, the answer varies depending no your tour location and the ease of getting new parts.
Ahh, I almost forgot, some latex gloves for messing with the chain.
I would add chain lube to the list.
I know you are not flying, but if you were you would need a pedal wrench, I use a short one as a compromise.