People are heaters. They produce heat at the rate of a light bulb: 100 watts more or less. Problem is, you can't plug them in. You can't shovel coal into them or petroleum products. You can't even use wood!
You have to feed them FOOD. Moreover you have to feed them food at a rate of 100 watts, day and night, week in and week out, month after month, year after year, decade after decade or they stop heating. Once they get cold, they stay that way -- forever.
R. Buckminster Fuller once opined that a major technological advance would be the production of a wearable life-support system for humans powered by solar energy.
OK, I don't have that designed, but here's the next best thing:
Well there's more to it but that's the foundation for the rest because eggs provide the key ingredient that enables you to consume the rest of your calories in relative health:
Moreover eggs do it with virtually no capital costs, no labor and no land.
Here's what you do:
Prepare to move to an old farm house (you have to live somewhere anyway), that's at the end of a dead-end road, or that has about a quarter-mile driveway setting it back from the road. (We're assuming food resilience is a priority in your life here.) You can find a lot of them vacant in the midwest due to the decimation of family farms. You'll save on rent or mortgage but that's just garnish on the soufflé.
Get a Great American Cattle Dog puppy and spay or neuter it. (This is a hybrid and hybrids don't make good breeding stock unless you're well versed in the techniques of terminal and rotational cross for heterosis.) If someone is advertising a litter and you want to save money (they can run hundreds of dollars) there is a chance that the last of the litter sold will have purely cosmetic defects, such as asymmetric markings on the face. Cosmetic defects are no handicap for a working dog.
Raise the dog for a year while you're preparing to move to the old farm house.
The first April that you're in the farm house, order 50 chicks of some heritage breed (or an assortment of heritage breeds) from a place like Sandhill Preservation Farms. OK, so these chicks aren't for free, but we'll get there soon enough.
Get two rectangular garbage cans with a hinged lid.
Get a few live roosters from a farmer that was gong to kill them. Before turning them loose, put one of the garbage cans next to your house, on its side, with the lid propped up like an awning. Choose a place where the storm winds are minimized, and weigh it down with something like a cinder block placed at the entrance length-wise. At sunset, put bread crumbs in it and watering dish just outside it, and place the roosters in it gently so the roosters get the idea its a nice place to stay for the night. This is your initial "chicken coop". You probably won't have to take out a second mortgage. They'll come back to that can every sunset.
Your dog is a hybrid of very obedient and intelligent herding breeds so a simple "no" should suffice if the roosters seem like toys to the dog. You won't have to repeat yourself very many times before the herding instinct kicks in and your roosters have a protector. On the other hand, as frequently happens, the roosters might get the "I'm not a toy!" message across on their own.
When the chicks arrive, introduce your one year old dog to the chicks. This may take a bit more convincing that the chicks aren't toys but not much. You'll get help from the roosters as they start to think of the chicks as part of the flock.
Place the other garbage can a short distance away from the roosters' can, with the cinder block weighing it down from the inside. Let its lid hit the cinder block to maintain just enough room for the chicks to get in and out of the can. At sunset, place the chicks in it, similarly equipped with crumbs and water. They'll huddle together at the back end to keep warm. When they come out in the morning to start grabbing insects and whatnot, they'll have imprinted on the can, and come back to it every night.
Never again let your dog in the house between sunset and sunrise -- not even -- especially not -- on the coldest winter nights. They're cold-tolerant. Just make sure they have a nice warm dogshelter or pet door into your garage.
At this point, you'll have a little ecology set up for the maturation of the chicks:
Roosters protect the chicks from birds of prey, as well as the dog "playing" with them. The dog protects the roosters and the chicks from predators like coyotes, foxes, etc. The humans feed the dog and provide them with territory to play out their instincts. All the critters in this ecosystem will be doing what they enjoy.
During the summer and early fall, build a leanto against your house, positioned to hit the house over a window so you can look out the window and see the inside of the leanto. That will house your flock for the winter with fulltime observation and additional light (for egg production) and heat.
You shouldn't have to feed your chickens unless snow is on the ground. You'll lose some of them during the winter. That's animal husbandry for you. It also may strengthen the "breed" so you can start incubating eggs laid during the winter for next year. I use "breed" cautiously here because there is no control of mating here. Uncontrolled hybridization tends to produce very unreliable results in the second generation and beyond. You can also end up with some roosters doing most of the siring while providing nothing in the way of the qualities you need for resilience. The best way to counter the rooster problem is to subject the roosters to more rigorous winter conditions. That way they'll die if they can't feed themselves and survive the cold. Sorry, that's animal husbandry for you. Again, this is of concern only if you want to truly "get your chicks for free" by hatching your own.
Now back to those 100 watt heaters.
The foundation of calorie intake is adequate protein intake. Forgetting about calories for the moment, just to maintain your body tissue, if you're a 220 pound man, you need a minimum of 3 ounces of protein a day and that protein has to be of a type that your body uses to build tissue.
That's a dozen eggs a day.
"Ridiculous!" you say "Eat a dozen eggs a day!?!?"
Just a second -- we're talking about food resilience here: the minimum requirements to make it through a severe disruption of food supply. That 3 ounces of protein doesn't supply the 100 watts required by that 220 pound man, but it does enable your diet to healthfully include a broader range of foods to supply the needed calories. Moreover, at 70 calories per egg, this 220 pound man is more than a third of the way to avoiding starvation, with 840 calories from that dozen eggs.
This 220 man has lifted a finger to collect those eggs, but not much more labor is required.
Its a lot more work to grow a garden than you might think. In fact, let's talk about what it takes to feed that 220 pound man on a garden alone:
Sunlight in temperate climates is about 100 watts per square meter average. If that man could eat pure sunlight all the time at 100% efficiency, he'd have his caloric requirements filled. But he's not photosynthetic. Plants are only about 1% efficient at turning sunlight into biomass. A typical garden captures at most about 50% of the incident solar radiation. Only 50%, at most, is edible, and plants can grow, at most, only half the year without very expensive greenhouse equipment with high operating costs. They also require substantial human work (calories) to work a garden, including all the ancillary tasks, so now you're suffering as much another reduction in effective solar conversion efficiency, but we'll ignore that and pretend you have an advanced solar-powered gardening robot or trained chimp or something.
So multiplying that all together:
100W/(.01*.50*.50*50) = 80,000W of solar energy
At 100W/m^2, we're talking 1800m^2 which is a gardened area about 100ft by 100ft and more like 200ft by 200ft if you include things like walkways. That is a BIG garden.
This is why agriculture has been heavy on the starch: Very high density calories both in terms of mass and in terms of production per cultivated land area.
So how much land area do you need to cultivate for your chickens?
Your yard in the country.
That's the magic of the protein gathering process:
The chickens are like vacuum sweepers clearing out the yard of insects. This wide-open-space, free of insects is filled as nature does a vacuum -- by more insects. So your chickens are really gathering photosynthesis, in the form of bugs that eat plants directly or indirectly, from miles around into your eggs!
Whatever else you do to in your food resilience architecture, eggs, done right, are a great high-return-on-investment cornerstone.