I worked in one office that had an entire barrel full of emergency supplies. I saw with my very own eyes that those included a fairly decent supply of N95 masks. We also had fairly regular earthquake drills, in addition to the occasional real earthquake. It is just possible that this is not typical of the average office.

I always kept at least a spare shirt in my car, along with a sleeping bag, a few canned goods, water, etc. The practice paid off a few times. Supervisors tend to appreciate employees who are flexible and adaptable.