A pandemic that's substantially worse than COVID-19 is a serious possibility. If one happens, having a good mask could save your life. A high quality reusable mask is only $30 to $60, and I think it's well worth it to buy one for yourself. Worth it enough that I think you should order one now if you don't have one already.

But if you're not convinced, let's do some rough estimation.

COVID-19 killed about 0.2% of people (20M of 8B). The 1918 flu killed more like 2.5% (50M of 2B). Estimating from two data points is fraught, but this gives you perhaps a 0.02% annual chance of dying in a pandemic. Engineering could make this much worse, especially given progress in AI, but let's set that aside for now to make a more conservative case.

A reusable mask ("elastomeric respirator") would be really valuable to have, if things got really bad. Let's imagine they cut your risk of dying by half: the rated efficacy is much higher (99%+) but real-world use isn't perfect, especially over the months or years another pandemic could last.

A mask should last at least ten years if unused, and over that decade it would drop this conservative estimate of your risk of pandemic-induced death from 0.2% to 0.1%. If you, as the US DoT does, value not dying at $14M, then this is worth $14k. Even if the benefit of a mask is 100x lower than we estimated ($140), it's still worth it to buy one.

I like geeking out over masks and there are a lot of options. I have a bunch of models, and if you'd like to come try them sometime (next EA Boston meetup on 10/26?) I'd be happy to show you what they're like. But if you just want to pick one and be done with it, leaving it in a box that you more likely than not don't need to open, a time tested but somewhat garish option is the 3M 6200 mask in Small ($17), Medium ($15), Large ($19) plus a set of 3M 2091 p100 filters ($7/pair):

I'd also recommend buying one now instead of trying to notice when a pandemic is coming: buying now ensures you get one instead of scrambling when everyone else is competing over a supply that can't keep up, and everyone who prepares ahead of time helps reduce shortages when a disaster comes.