Would you take a cookie?

I was walking through a building on my way home from a night class last week when I saw a table set up as if for a reception. It had cookies, punch, and I think a cheese tray. Nobody was around... I had no idea what all of that food was doing there, but I could have walked off with the entire table if I had been so inclined. However, I did not take a single cookie, cheese cube, or sip of punch. Why didn't I? This has me thinking, am I not a utility maximizer? If not, is it because of moral conviction against theft... or was I just afraid of being caught with my hand in the cookie jar? (I was starving at the time, by the way... the class ends at 8:10 and I usually don't eat dinner until afterwards).