What can I do with old windows to keep heat in?

Yes I used that shrink fit plastic

Yes, it does. I recommend insulated curtains, too.

Insulated curtains make a big difference.

If you have windows that are not used to see out, one method I found effective is to use bubble wrap. All you do is cut the wrap to fit, spray the window with water, and press the wrap in place. Can be peeled off whenever your ready. I have cafe curtains on a bay window in my kitchen that I almost never open. The bubble wrap prevents the cold air from seeping through.

For other solutions, a Google search turned up a few options: https://www.google.com/search?q=keeping+heat+in+old+windows&oq=retain+heat+in+old+w&aqs=chrome.1.69i57j0.7877j0j7&sourceid=chrome&ie=UTF-8

Also, check out YouTube: https://www.youtube.com/results?search_query=insulate+old+windows+for+winter

Yes the window kits plastic does really work. We have older windows on the one side of our house and apply this every winter. It has been a life saver. Insulated curtains do make a big difference but unless you keep them closed all the time you are going to feel the cold when open. They are a great additive to use with the plastic.