Polarising filters can be an essential part of a photography tool set, as they suppress glare, make blue skies pop and offer an additional way to control the light in your scene. And if you have some old electronics that you can mine for spare parts, you might already have a filter.
It turns out the glass screens on old liquid crystal displays that you can find on something like a calculator or an old Nokia phone have a transparent layer that acts as a polarising filter. If you disassemble the device (and are careful not to break the screen, of course), you can use it as a rough but ready polarising filter. Obviously such a small screen won't work with your DSLR, but you can experiment with your smartphone camera to see how the filter works. (You can also try shooting photos through your sunglasses if you have polarised lenses.)
This tip comes from the Koldunov Brothers, who often find unique ways to use household items in photography. It certainly isn't a professional solution to making a filter, but it's a fun way to repurpose any broken electronics you might have lying around.