A somewhat absurd but perhaps useful project: a completely non-electric fog machine. I have seen DIY electric fog machines that are very difficult to make and/or that consume a lot of batteries because they need very low electrical resistance to reach high temperature. So I made this alcohol-powered one using cans, silicone adhesive and a cheap bellow horn.
Warning: Glycerin is non-toxic, but prolonged exposure to its vapors may cause respiratory irritation.