A stretch:
Obviously there was plenty of (hot) food for guests at the wedding, as in "You like your lasagna?" But perhaps the Great Sandwich Toss was FFC's way of reinforcing that Paulie wasn't a guest--he was a hired hand (as in Clemenza testily reminding him that he wasn't a dance judge, and to walk the neighborhood and do his job--and therefore Paulie wasn't entitled to sit and eat with the guests. And maybe the sandwich toss reminded him of his second-class status and pissed him off.