As others have said, broken chains are rare, I have had one in 20 years or so. On that occasion, no-one had a chain tool, so it meant coasting and pushing back to the start. A lot of multi tools have a chain tool, so that's taken care of, a suitable master link ( make sure it matches your type of chain ( up to 8 speed, 9 or 10 speed ) SRAM are popular, and you can deal with pretty much any chain problem. You might end up shortening the chain, but that just means you have to be a little careful with the shifting.