Before our office moved, we had a great kitchen/lunchroom (in our new location we just have a litchen, but no place to have lunch except a boardroom). A group of us started "Salad Club". We would each bring in an ingredient, and one person would volunteer to bring in lettuce. So we would always end up with a great variety of ingredients and fun salads every day (no two days ended up being alike). It was cheap, cheerful, and social.
Occasionally we would have ingredients that didn't go so great together or duplicates, so we'd keep it for the following days. We had vast kitchen cupbaords that were mostly empty, so the Salad Club had a little shelf set aside for canned goods.
Eventually we realized that someone was pilfering our food. At first we were sympathetic, because it meant someone was hungry. We assumed it was a student hire or someone else in need. But in time, it got ridiculous! We were practically being cleaned out! Finally another co-worker, "Bob", overheard someone on the phone (open concept office) making plans with her hubby to have hot fudge sundaes for dessert that evening, and referred to the chocolate sauce in the office fridge. Bob's chocolate sauce. Sure enough, Bob's chocolate sauce went missing.
Bob knew who the thief was but couldn't prove it. So without identifying the culprate, he did tell us that someone who was not "in need" was likely the one taking our salad supplies.
To end the thieving, we peeled the labels off all our canned goods. We used a marker to write a number on the bottom of each can, so we knew what the cans contained, but the thief never touched them again.