I carry a weeks worth in at a time in my panniers, or on the trailer if it's too much to fit. For cold stuff I could carry an ice-chest on the trailer, but I normally don't. My work commute is not that long.

A long time ago I worked at a place that had a lunch thief. Until someone placed a big, human feces burrito in the refrigerator. No doubt who the thief was after that. He was the guy out back washing his mouth out with a hose for an hour.