The act of saying grace, typically done before meals, can also be done after meals.
This particular tradition pre-dates Christianity, and according to The Sacramentals of the Holy Catholic Church by Andrew Lambing, giving thanks after meals to God goes all the way back to Moses.
Early Christians adopted this practice, and over time it became common tradition among Catholic homes.
In particular, many homes would remember the faithful departed at the end of each meal.
Here is the most common Catholic version of saying grace after meals.