Which I do on longer rides, but they only seem to break on casual rides when I don't have them.
But I've also broken frames and taco'd wheels. Should I bring spares for those?
That generator can probably do a million miles.
You must be putting your bikes through hell and never maintaining them. There are no instances where a chain should break if properly maintained and replaced at the end of its life.
It's happened twice. Once was on a really old chain. The other I'm not as sure. I'm a heavy guy. If I use my weight I can put a lot of torque on the pedal.