The Prayer Before Meals has a purpose, beyond grace (which is important).
When we eat food, we are prudent and wise to first remove it from the dominion
of satan, the "prince of this world." We do that by blessing the food, "Bless us O Lord,
and these, Thy gifts..." This is from Apostolic times, taught by Our Lord Himself,
and passed on through the ages.
You can read fragments of this principle in Scripture when they mention
meat sacrificed to idols. We do not know what dedication or prayers have
been said over the food that we're about to eat, especially when it was prepared
or marketed by someone else. Our blessing removes any hold the devil has on
the food we are about to consume. Remember that your food becomes part of your body, so if you don't bless it, you'll be carrying around your body with cells that
have material that was possibly dedicated to the devil.
After meals, it's traditional to end with "We give Thee thanks, almighty God,
for these and all Thy benefits, Who livest and reignest forever and ever, and
may the souls of the Faithful Departed, through the mercy of God, rest in
peace. Amen."
In traditional monasteries, they read from the Martyrology during meals.
This keeps our minds focused on the ultimate purpose of eating, bodily sustenance,
and on our need to forever be vigilant. For without this perspective, the
taste and pleasure of eating can easily become a sort of false god in itself,
and we fall into gluttony. It is quite natural for our fallen nature to overtake us
this way. Thinking about the martyrs, who gave their lives for the Faith, helps
us to avoid gluttony, one of the seven capital sins.