The two most popular Catholic prayers that surround food traditions are the simple “Grace Before Meals” and “Grace After Meals.”
One need not pray these prayers on Thanksgiving if you are Catholic, prayers from your own words are, of course, fine.
However, if you are looking for more structure in your prayer these two simple ones work well.
Grace Before Meals
Bless us O Lord and these thy gifts which we are about to receive from thy bounty, through Christ Our Lord. Amen.
Grace After Meals
We give Thee thanks, Almighty God, for all thy benefits, Who livest and reignest, world without end. Amen.
While Grace After Meals is seldom ever prayed it indeed does express Thanksgiving. The Eucharistic prayer at mass is the church’s big prayer of Thanksgiving (which is what Eucharist means). So as it is prayed at mass think about what you are thankful for each week and that might help you put together what you’d like to share around the table on Thanksgiving Day.