On the rear end of my single speeds, I am a fan of V-brakes, horizontal dropouts and solid axles with 15mm nuts. Set it and forget it. No creaking EBB, so slipping sliding dropouts, no fussing with disc brake adjustments. Simple and effective, if not a bit crude.
Consequently, this requires that one carry a 15mm wrench. There are a few made by single speed companies, like Surly, but they are short and too damn expensive. Really, $30 for a wrench? So I can open a beer with it?
I prefer a nice Craftsman wrench. Nice and long for leverage, six-point to keep your nuts from rounding, and at a cost of eight bucks from your local Sears. Throw it in the Camelbak and forget it.
Oh, and with practice you can still open a beer with it and show your single speed attitude.