probably one of those super bright one AAA battery keychain flashlights (~$12). Because its attached to your keys you always have it with you, and the smaller

probably one of those super bright one AAA battery keychain flashlights (~$12). Because its attached to your keys you always have it with you, and the smaller and brighter flashlights get, the more useful they become somehow. I'm not kidding, these things are blindingly bright.