What is the manna of the Old Testament, which was food for the Israelites while in the desert? What kind of food was it?
Num 11-7 Now the manna was like coriander seed, and its appearance like that of bdellium.
Exodus 16:31 Now the house of Israel called its name manna; it was like coriander seed, white, and the taste of it was like wafers made with honey.
Put simply, it was bread.
This bread was a foreshadow of the Euchurist, a foreshadow of the New Covenant and a foreshadow of Christ.
Today, as it applies to Christianity, this Bread is the bread of life, the fruit of the tree of life, the true manna from heaven, Christ himself body blood soul and divinity. It is the Sacrement of Sacrements, the source and summit of the Christian Faith.
From Lumin Gentium Taking part in the Eucharistic sacrifice, the source and summit of the Christian life, they offer the divine victim to God and themselves along with it.  And so it is that, both in the offering and in Holy Communion, each in his own way, though not of course indiscriminately, has his own part to play in the liturgical action. Then, strengthened by the body of Christ in the Eucharistic communion, they manifest in a concrete way that unity of the People of God which this holy sacrament aptly signifies and admirably realizes.
The chosen people of God rejected the Manna in the old testiment just as many Christians today reject it. As Israelites made the manna into cakes and wafers so to does the Catholic Church, however, the wafers are made now prior to the Holy Spirit Changing the bread and wine into Christs body and blood.
It was bread for the body but has become bread for the soul.