For short stops like that I carry a thin, lightweight cheapo lock. I don't have very valuable bikes, and I figure anyone who might pinch a bike on a whim like that is not going to be carrying a humongous lock cutter around. It's not hard to cut a lock, but you can't do it with standard home tools, at least not the ones I have.
Bikes that are regularly locked up at the same place and time, or left in a spot with many other expensive bikes are definitely at risk from the professional thieving lot though.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett