Broke my chain today at Calavera, but luckily I was behind the water tower where there happens to be a pretty decent machine shop*.
I didn't have a chain tool but I did have a multi-tool which is almost as good except for breaking chains. Luckily I was able to put together a makeshift press and get the broken link off:
Unfortunately I had to take about 10 links out to get the master link off so it was single speed the rest of the way out. I'm kinda hardcore though so I only had to walk about 10 times. There's big hills out there!
*rusted out car