It all depends, but for me, getting to work on time is a priority. Other people depend on me showing up on time, just like I may depend on them. Arriving late because of lacking tools to fix a simple puncture isn't something I want to do. A bag and a repair kit (spare tube) is just a small but necessary expense for me. I prefer to be in control on when I arrive at work instead on relying on random luck.

You should ask yourself similar questions; does it matter that you arrive late at work? Is walking 3 miles home in the rain an acceptable risk? What are your options if you puncture, bus, cab, walking?