My west coast tour was marred by broken spokes. I made it halfway before I broke the first. Towards the end I was breaking one about every other day. When they would break I'd put an emergency spoke on, true the wheel to the best of my ability, loosen the quick release on the brake, and ride to the next bike shop, where I'd have them replace the spoke. It was a huge pain, I wasted a lot of time waiting for repair people to have time to service my bike, and it got pretty expensive.
Background Info: I was riding a mail-order bike - a touring model from Nashbar. The 36-spoke wheels came preassembled, and I never took them to a bike shop for a tuneup. I weighed about 210 pounds, and carried a lot of heavy stuff - too much. (Since then I've replaced my tent and sleeping pad with lighter versions, and I've learned to carry much less stuff. I also think I'm down to about 200 pounds. I still have the same bike though. )
I'm looking for advice from mechanically knowledgeable people before my next long tour. Here are some options I've considered. Please consider commenting on them, or suggest your own.
1) Buy a cassette-removing tool, learn to true a wheel (is it possible to do on the road without a stand?), carry extra spokes, and repair broken spokes myself on the road.
2) When spokes start to break, go to a bike shop and replace the rear wheel entirely. (Can you get a good touring wheel at a local bike shop off the rack, or do you have to order something?) Although this seems expensive, my experience on that west coast tour tells me that spending a bunch of money all at once for a new rear wheel would probably be less expensive than all the money I spent getting spokes replaced over and over. Interestingly, there didn't seem to be a standard price for replacing a spoke and truing a wheel. The cost varied widely, and they could often be dickered into doing it for less than the price they originally quoted.)
3) Prior to the tour, go to my local bike shop and ask them to build me a bullet-proof rear wheel. (Is there such a thing?)
4) Get a Bob trailer.