We lost power here in Bernardsville for some 58 hours last weekend. Since our home has gas-heated hot water baseboard heat, and the outside temperature was around -13C, I was concerned about having a frozen water baseboard heating system. The furnace has 4 75W circulating pumps, plus electric gas ignition.
So I disconnected the furnace from the mains, and plugged it into a 650W inverter purchased from Walmart, and connected the inverter to my idling Miata for some 30 hours. We had a warm, comfy, dark house, with enough spare power to charge batteries, run the DSL line and a laptop, and even turn on our outdoor LED Christmas lights ("survival with style").
The Miata was fine. The guys on Car Talk point out that cop cars idle for long periods of time without harm: we aren't using carburators any more. It got zero miles per seven gallons, more if I ran hi-test.