I carried a chain tool for years before deciding I just didn't need it since I was light and low power, so I would probably never break a chain. About a year later, I dropped my chain and got it stuck in the crank arm while trying to pedal it back on (fast group ride, I didn't want to get dropped). That kinked 2 links in the chain and I had to borrow someone's tool. Now I have the Pedro's multi-tool that includes a chain tool and tire lever in it. Although a bulky and heavy tool, it actually takes up less space than supplementing a smaller one with a seperate chain tool and tire levers.