Umm, lighting. This time last year I was all about a system mounted completely on my head.
I don't even know what emotion was driving this state of mind, but the whole concept seems seriously disturbing now, just a year later. Not to mention that I blinded some really good friends. The light is back on the bike, where it belongs and I have a whole 'nother spare helmet that I can use any time of day or night. And my neck isn't killing me. Sweet.