Let's say the mega-earthquake comes and you're stranded with just some MacGyver-style bits and bobs. If you've got a magnet and a little knowledge, you can make a compass that reliably points north. Below, check out a vintage segment from Curiosity Show explaining how to do it—and a bit on the science of why compasses work.
In the clip below, presenter Deane Hutton shows three methods involving a mirror, cork, a pin, a drinking straw, and a circular magnet (in different combinations). There's something for everyone!
Incidentally, one of the key issues in making a compass is knowing which end of a magnet points north and which points south. One YouTuber asked how to determine this, if it's not already marked—as might be the case in a survival situation. Decades after the clip aired, Hutton chimed in via YouTube comments to answer:
Wait till the Sun is about to set. Stand with your right shoulder toward the setting Sun. You are now facing South. Suspend the magnet and let it swing freely. When the magnet stops swinging, the end pointing South is the South Pole of the magnet. Deane.
Science is cool. Anyway, enjoy: