I never broke a chain, but I once broke a rear derailleur cable 8 miles from home in the pre-cell phone era. Luckily the multitool I had included a chain tool, so I opened the chain, pulled it off the rear der, and rewrapped it onto the small ring and the largest cog I thought I could push on the hills I needed to climb,removed the necessary links and road home as a single speed. Now I always carry a chain tool in my bag.

But now I also always carry a cell phone, too.