Most of the country side in the world is outside the USA, where a hunting rifle is the most people would have, if anything.
This is a smart instinct, but the ammunition only lasts so long. Someone deep in the boonies with a good stash will be okay, but anyone within 1-5 day's march near the cities had better be prepared to "stack 'em high' for a long time before the stream of starving city ex-pats slows to a trickle.
You'd probably be surprised by the number of folks who have tens of thousands of rounds. When ammo prices started going up, pretty much everyone I know who shoots at all started buying in bulk. Not saying everyone who has a gun is trained or mentally prepared to shoot trespassers for months on end, but I think a lot of people who think farms and ranches will be easy pickings haven't spent enough time with the folks who live out here.
I shoot recreationally, two guns in the same caliber, maybe once every two months, and have 4-5k rounds stacked in the closet.
If you shoot often, and have multiple guns in multiple calibers, 50k rounds is not difficult at all, especially if you have anything "weird" where you will likely buy as much of the ammo as you can find.
What are people's opinions on crossbows as supplemental defense weapons? They lack range and ammo is not compact but they are quite stealthy.
It really depends on how long the power is out. Crossbows were a fearsome weapon of war during the time in history when guns still weren't that accurate or easy to come by. If there's a gap between "people using manufactured ammunition they stockpiled" and "people figure out how to manufacture ammunition and gunpowder reliably like they were in the 1800s before power was ubiquitous", then a crossbow would do quite well.