I didn't mean that your question was a joke, but that the product itself is.
Now, propane is a much more efficient heat source than charcoal or wood, if you look at it as a BTU/volume ratio. That being said, there are some advantages to wood and charcoal (particularly wood) in that you can continue to find them after a SHTF scenario.
How much propane? That's a lot like asking "how much water" or "how much food?" If you expect the interruption in services to last a relatively short time, and the only thing you;re using propane for is heating food/water (not running a generator), 10 gallons should be sufficient. I figure 5 gallons a week is enough to cook 21 meals and boil a couple of gallons of water per day. That's based on years of backyard bar-b-queuing, not on recommendations from outside sources. If you see yourself becoming the center of civilization for your neighborhood, you might want to think more along the lines of 5 gallons per day.
Propane lighting doesn't take a lot. A little Coleman-sized can will keep a single-mantle lantern burning most of a night. You can buy adapters to refill those little cans from a larger tank (although I've never tried one). I'd estimate an extra gallon a week for each lantern.
Propane generators, well, that's a completely different beast. Consumption rates would be available in the instruction manual.
I once lived in a house that had an outside propane tank. It ran the stove, oven, hot water heater, bathroom heaters and central heat. It was in to 250 gallon range. Typically, we'd fill it once at the start of winter, and again at the start of spring. That 250 gallons would easily last the 8 months of spring-summer-fall, and keep us comfy-warm all winter without threat of running out. Peak consumption during non-heater months was around a gallon a day.