I know grandma fed her dogs on porridge (oatmeal) and table scraps. They were all on the fattish side of healthy, and all lived 15+ years. I have accustomed my dogs (one 60 pound mutt, one mastiff) to eating table scraps routinely, and porridge for a treat. I believe they will make the transition to straight table scraps and porridge pretty easily, if the need arises. Now, I stockpile a few bags of (rather pricey) dog food, and a bunch of (very cheap) oatmeal.
For the cats, I am not quite sure, yet. The younger ones will become mousers, but my old guy (15 years old) might just not make it. If we had chickens, I'd feed him on scrambled eggs, but he's too arthritic to hunt, and the arthritis is in his jaw, too, so he doesn't chew too well. Given that he's outlasted several long-term boyfriends and a few jobs, as well as three inter-provincial moves, I'll do my best to keep him healthy and with me. If it's so bad that I really have to quit feeding or abandon my critters, I'm not sure how badly I'd want to survive it...