When I told the lady at the other end what happened, she said, "I'm sorry - if that's the right response." I asked her what I should do with all these extra cokes, and she said, "Well, I guess if there is no one to turn them in to, you can just keep them." Too bad I don't care for Diet Coke, but it's good that people in my office do.
Afterwards, an older gentleman who saw the whole thing said, "that was very honest of you." But really, was this anything special? It's too bad that doing the right thing doesn't seem normal.