When this topic or variations come up, the obvious common calibers get listed as the best to build around. I can’t argue with that, but I would also suggest that having some guns in slightly less common calibers might help you out.
I know we’ve all seen that whenever we have an ammo shortage, the oddballs are the last to go. But I’ve noticed that some not-so-odd ones stick around. I’ve seen .270 and 7mm Rem Mag on shelves long after others were long gone. The .243 Win and .25-06 last almost as long.
Reloading could help beyond imagination. Besides the obvious things, reloading might sometimes allow you to make something out of nothing. Find some .243 but can’t use it because you have a .308? If you reload, you can re-form it. That’s something in favor of selecting cartridge(s) belonging to a “family” instead of those that are more unique.
If you reload, consolidating on one bore size might help stretch things a little. If you have .308s, .30-06s, and .300 Win Mags for example, you could now be stocking up on one bullet for them. For example, buying .308” diameter 165 grain bullets whenever there’s a sale gives you a stockpile that will work fine in any of them. Even the weights we’d normally consider specialized, like 110 grains in this .30 cal example, would at least keep you shooting.
That applies on a bigger scale to casting your own bullets. A nice stockpile of lead can become bullets to feed anything if you have a variety of moulds. Even slugs, buckshot, and airgun pellets. I would sure work out those loads now, though.