One of the most useful and handy machine that you can keep at your house and that will help you make your house comfortable even during the winters is a used insulation blower. It is a machine with which you can fill the cavities in the wall with insulation materials such as rock wool, fibre glass or cellulose.
You can blow out the insulation material directly into the cavities from the container and spread it out up to a desirable height. Used insulation blowing machines are cheap and easy to get. If you find one in good condition it might last you your lifetime.