Cookie Monster

So The Boy and I stopped at the Quick Trip on our way home from playing to get gas and something to drink. For two seconds I took my eyes off The Boy, and when I found him again, he was eating a giant cookie from the bakery case. So we also bought a cookie. He didn't know it was wrong, and I had no idea how to broach the situation so I remained silent. Ideas from more experienced momma's?
Frankly I'll take this situation over yesterday's (nuggets in the bathtub...).