Keys

Keys are the coolest thing ever. The "key and lock" system of technology (from ancient to modern) is really, really great.

Keys open things that "require security for some reason". Doors, chests, lockboxes, fucken trapdoors... dozens of lockable possibilities. But the best concept is what's inside. Endless potential. I'm totally going to "lock something away" right now, purely for the novelty value of it all.

Editor's Note: wearing a key as a pendant around your neck is pretty awesome, too.