I am a firm believer in having at least two main calibers at hand, both for rifles and pistols. In my case it is 9 and 45 for handguns, simply because I am invested in 1911s and love them for what they are. 9 and 40 makes more sense though if somebody wants to use similar pistols.
These are strange times. I am sitting on a shitload of ammo and I so far refused to slow down my shooting schedule. This ammo run and drought may be the longest we've seen though.