I leave my bike unattended a lot, but NOT unlocked. Sometime you just have to be resourceful. We were staying at a hotel with a low security parking garage and bikes not allowed in rooms.
I fabricated these 3/32" security cables for my Classic Ortlieb Roller panniers. It is similar to the ones they sell for the Packer Plus series. They will not stop a professional thief, but they will discourage the opportunistic thief. Sometimes if we are going to leave camp for a long time we will cable all the panniers together, which make for a pretty unwieldy load. My wife and I both have these on our panniers, but we hardly ever use them.