I typically yank the hard drive before sending a PC for recycling. SOP.

The spinning disc inside the sealed hard drive is made of metal, with a highly polished surface (deposited magnetic recording medium) and a hole in the middle. In terms of reflectivity, IMO it is significantly better than acrylic mirrors, and darn close to glass.

This makes a very high quality, easy to aim, improvised signal mirror. Plus, the other metallic components (moving arms etc.) would make excellent fishing tackle. I you hack one of these apart in the bush and show your scouts what you can do with the internals, you will absolutely blow their tiny minds.