Truing a wheel and lacing spokes is a big deal, but even a novice like me can replace a spoke and get it good enough to ride if a single spoke breaks. Unless you have a really low spoke count (which seems unlikely on a tour), breaking a single spoke shouldn't make the wheel unrideable and replacing the spoke can improve things and prevent them from getting worse.
Spokes are light and can be slipped down the edge of a bag or taped to a tube.
Things are made a little more complicated if the broken spoke is next to your disc or cassette. If so you may not have space to lace the new one in. In that case you'll need the tools and expertise to remove the disc or cassette too.
I've heard you can often get away without a spoke or two if you adjust the adjacent ones (loosen on opposite side to broken one, tighten on same side). This isn't a long-term solution, but may be good enough to get you home.