The ideal house is one snuggled into the South side of a hill, with windows facing the sun.
But most of us cannot afford to build something like that, especially nowadays.
Nor can many of us afford new insulative triple-wall windows, at least from an upfront cost. They will eventually payoff, but that's way down the road.
However there are quick and dirty ways to help insulate.
About 20 years ago I lived in a nice, humble, trailer up on a hill here in Reno.
But in winter, the cold spilling in from the windows was miserable.
I had a good sized piece of bubble wrap, and decided to cut it to fit in one of the windows.
Immediately the cold went away. Well, at least lessened most significantly.
After hunting around, I was able to Bubble wrap all my windows, and the place became much more pleasant.
No more nasty cold spots.
And my power bill was reduced.

My kid is now in the same situation, and tonight I ordered some rolls of wrap to put in his domicile.
I'm getting half inch bubbles, because I feel they let both light and outlines in very well.
The smaller bubble wraps work well also, and are cheaper, but make things ouside seem just more...fuzzy.
The 1/2 inch runs about 25 cents a square foot.
The 3/16 is around 12 cents a foot.
That's in bulk, and retail is certainly more costly.
Tho' much of it can be had for FREE by recycling!

From poking around the internet, I read on various sites, that BW can save heating costs around $1.60 a square foot. Now I don't know if that's per month or per season, but to save $1.40 a foot by spending an initial 12 or 25 cents, makes sense.
Of course, I don't know if that figure is true,and don't have the schooling to figure that out.... But I can feel the difference.
Bubble wrap will last several years. The optical quality will diminish a bit in sunlight after awhile, but it still works great.
I cut it to size, and then spray or wipe a little water on the window, and brush on the wrap. It should stay in place pretty much by itself.
Someone suggested putting some glycerine in with the water, which I haven't tried. A spot of oil might work also?
I know that for odd shaped windows, you can put just a bit of double sided clear tape between window and wrap, and it holds just great.

Now while BW is made from petroleum products, I suggest that the savings in NOT buring extra Fossil Fuels to heat by using bubble wrap is a very positive EROEI.
The cool thing about this stuff, is that it lets great light in, yet diffuses images so that you have some real sense of privacy.
Also, it is easily and quickly taken down, and put back up.
If it's a nice sunny semi-warm day, take it off, and let the sunlight and energy in more fully.

BW will also work in summer, to miniscule-ly reduce solar gain, and keep cooler air in.
Of course, in summer the big idea is to prevent solar gain.
The kid had a condo awhile back, before the housing crisis, that had a glass patio door facing due west.
By my calculations, the heat gain through that door was the equivalent of running a 1200 Watt electric heater.
And, this is in the summer.
The quick fix for this is installing an outside shutter of some sort, or hanging material to block the sun.
In a real quick and dirty manner, you can put aluminum foil on the OUTSIDE of your windows.
Billy shaded his outside windows, and said it 'significantly' lowered his cooling bills.

And, a final word about bubble wrapping windows. If they have aluminum frames, it is worthwhile to insulate them also. Aluminum is a fast heat transferrer, and by only covering the glass, you have not achieved maximum insulation.
In addition, you can do double layers of wrap, and with a bit of glue can make two panels into one.

We can make these fixes, and reduce our consumption quickly and cheaply by expanding on and using these ideas.
When you try this, please share the reductions in your winter heating costs. It would be nice to get figures on this.

I also have tried plain cellophane wrap on windows. Unsucessfully. If I had a squeegee, it would probably work fine, and is MUCH CHEAPER than BW.

Thank you for helping us stave off collapse.
Craig

BTW, when you order your bubble wrap, get enough to help that neighbor of yours do his/her windows also.
The gift that keeps on giving.