Life as I know it wouldn't have come to pass without a computer, so I'm inclined to say that! Though, to say more on the subject...

I don't quite have a Book of Shadows set up yet, so that's a little embarrassing...

Uh, opposable thumbs?

I think I'd also like to say my bike! I don't particularly enjoy driving much and when I go out it's usually up to hours that public transit doesn't run anymore, so having a thing for exercise and transport both is really convenient. Especially so when the library and a supermarket are just 10 minutes away by it!