Well, maybe it's not quite as strangely dangerous as a pocket full of degenerate matter, but a 3" neodymium super magnet gives you almost science-fictive powers. As one of the strongest consumer magnets on the planet by weight, two of these coming together can break your fingers and require 700lbs of force to detach from each other.

Gaussboys sells a wide range of magnets, from tiny pieces the size of penciltips to monsters you can use to pull the dents out of cars. I wouldn't suggest using them to tack pictures to your computer, though.