Plastic or rather polyethylene tarps or sheets, even plastic bags, stapled to Windows around frame help a lot to keep house warm. Another very good trick, is to hang blankets in hallways that don't have doors. It keeps the room where the heat is warmer, and really really helps with drafts. That also helps to survive, if no heat anywhere, and to keep one living space warm To keep water in sinks bathrooms kitchens from freezing, keep the cabinet doors open, and if really cold, keep the water trickling, especially in cold water lines. These tricks can save your pipes from freezing, which is real mess and expensive. Source - Canadian.

I remember my parents covering my old leaky single-pane windows in our first house with plastic in the winter. It looks goofy, but it's cheap and it really helps. We also had storm windows that we'd replace our screens with in the winter.

We later moved to a house with newer windows that removed this need, and adult me has a ground source heat pump so I'm toasty even with the 15°F weather here.

Anticipating the cold snap, my wife ordered insulating curtains for the big windows on the front of the house, to hang behind the decorative ones.

I figured it was more an example of "must do something" than "activity that will actually help," but I was proven wrong IMMEDIATELY. They've made a material difference (no pun intended), and I'm said I said no when she asked if I wanted some for my office.

She's a keeper :)

Absolutely. We've been keeping each other for almost 20 years.

>would not make any financial sense.

Yeah, that's what people often miss. We're not prepared for this, and don't build for it, because it almost never happens.

And it'll be 70F on Sunday.

Bubble wrap produces very decent insulation for single-pane windows.