I actually had to cut today's ride short due to a broken chain about 30 miles in. First time I ever had that happen. The chain didn't actually break but the joining link has disappeared and I couldn't find all the parts of it on the road despite looking in the hope I could put it together again and continue. No idea why that should happen now as the it hadn't been disturbed in several years.
Had to hitch a lift of a stranger and drive back for the bike, hence being home earlier than planned.
I suppose the moral of the story is to carry a chain tool and a spare link but I've never done that with hub gears or singlespeeds as I always felt problems were more likely with derailleurs.