Many people heat their homes with electricity and when the grid goes down you must be prepared to stay warm on even the coldest winter nights. Hopefully most homes have a number of blankets, and everyone living in the home has some warm clothes (including fleece sweaters and pants, thermal underwear, along with some wool socks, gloves and beanies.) If everyone in the household is not equipped with these, this should be first priority.
One important part of prepping is having gear and supplies that are dual use. A winter sleeping bag works great for just this. You can use it for camping when it's cold outside, and also for when the heater goes out you can sleep in comfort. Mummy sleeping bags that are rated down to 0 degrees and less can be purchased for very cheap (compared to what you would pay at Cabelas). I purchased a High Peak Summit sleeping bag that's rated down to 0 degrees for $50.
Unfortunately that seller on eBay doesn't offer them at that price but Amazon sells the same brand of sleeping bags for around that same price. Don't let the price fool you the sleeping bag is very well made and extremely warm. I've camped with it down to around 20 degrees and never got the least bit cold. A mummy sleeping bag is great for camping but would also be great for those cold nights if the power were to go out for whatever reason.

