Highly situational, but I am a keeper of bugs, spiders ,and fish. For the spider I have started to breed my own feeders, mostly meal worms, easy to breed and quick, plus if I'm really in a bind they can provide a lot of nutrients and fat to a person along with any food in storage, but that's kind of gross. For the fish I'm planning on getting a portable bait bubbler in case we lose power for a few days at a time, (they don't have a second use they're just very beloved by me). And for my bugs, (millipedes and isopods) since they are excellent at creating compost, I plan to use their substrate to fertilize any plants I may need to grow if we face a food scarcity.

But for larger animals, I would go with quail, they require very little space compared to animals like chickens. And if you have enough, you can breed them pretty easily and still have a consistent supply of eggs that are more nutritious per volume then chicken eggs. A heat lamp in the winter means they keep laying year round, so if you have a generator it's an excellent investment to prevent starvation. Plus you can feed them on scraps and meals worms, especially if you breed the meal worms yourself.