The following is a well-known blessing:
"Benedic nos Domine
et haec tua dona
quae de tua largitate
sumus sumpturi
per Jesum Christum
Dominum nostrum
Amen."
It's possible that you might want to serve some authentic Roman recipes for Thanksgiving, but it's probably more likely that you'd serve a Thanksgiving Cornucopia. (Cornucopia derives from the Latin cornu, meaning horn, and copia, meaning plenty.