I have a U-lock that spends the week on the rack at work unless I know I'll spending time somewhere with high theft potential where I can't see my bike. That way I don't have the problem I used to have of riding my secondary bike to work and realizing that I forgot to grab the lock off of my main ride. The rest of the time I carry an OnGuard looped cable and feed one end into my ring lock after looping the other end around something stationary and through the front tire. It still requires me to carry something, but it provides enough security for me for 90% of my riding.