How does Garvey convince Cole to eat the groceries?

Garvey convices Cole to eat the groceries by saying that Cole's probably afraid of eating it. Cole doesn't want to be afraid of anything, because he thinks that everyone and everything has to be afraid of him. To prove that he isn't afraid of anything, he eats the groceries.

what were the groceries?

I believe they were ingredients for a cake. Food items like eggs, flour, salt...