Ignatius of Antioch
"Consider how contrary to the mind of God are the heterodox in regard to the grace of God which has come to us. They have no regard for charity, none for the widow, the orphan, the oppressed, none for the man in prison, the hungry or the thirsty. They abstain from the Eucharist and from prayer, because they do not admit that the Eucharist is the flesh of our Savior Jesus Christ, the flesh which suffered for our sins and which the Father, in His graciousness, raised from the dead."
"Letter to the Smyrnaeans", paragraph 6. circa 80-110 A.D.
"Come together in common, one and all without exception in charity, in one faith and in one Jesus Christ, who is of the race of David according to the flesh, the son of man, and the Son of God, so that with undivided mind you may obey the bishop and the priests, and break one Bread which is the medicine of immortality and the antidote against death, enabling us to live forever in Jesus Christ."
-"Letter to the Ephesians", paragraph 20, c. 80-110 A.D.
"Take care, then who belong to God and to Jesus Christ - they are with the bishop. And those who repent and come to the unity of the Church - they too shall be of God, and will be living according to Jesus Christ. Do not err, my brethren: if anyone follow a schismatic, he will not inherit the Kingdom of God. If any man walk about with strange doctrine, he cannot lie down with the passion. Take care, then, to use one Eucharist, so that whatever you do, you do according to God: for there is one Flesh of our Lord Jesus Christ, and one cup in the union of His Blood; one altar, as there is one bishop with the presbytery and my fellow servants, the deacons."
-Epistle to the Philadelphians, 3:2-4:1, 110 A.D.
St. Martyr
"This food we call the Eucharist, of which no one is allowed to partake except one who believes that the things we teach are true, and has received the washing for forgiveness of sins and for rebirth, and who lives as Christ handed down to us. For we do not receive these things as common bread or common drink; but as Jesus Christ our Savior being incarnate by God's Word took flesh and blood for our salvation, so also we have been taught that the food consecrated by the Word of prayer which comes from him, from which our flesh and blood are nourished by transformation, is the flesh and blood of that incarnate Jesus."
"First Apology", Ch. 66, inter A.D. 148-155.
St. Irenaeus of Lyons
[Christ] has declared the cup, a part of creation, to be his own Blood, from which he causes our blood to flow; and the bread, a part of creation, he has established as his own Body, from which he gives increase to our bodies."
Source: St. Irenaeus of Lyons, Against Heresies, 180 A.D.:
"So then, if the mixed cup and the manufactured bread receive the Word of God and become the Eucharist, that is to say, the Blood and Body of Christ, which fortify and build up the substance of our flesh, how can these people claim that the flesh is incapable of receiving God's gift of eternal life, when it is nourished by Christ's Blood and Body and is His member? As the blessed apostle says in his letter to the Ephesians, 'For we are members of His Body, of His flesh and of His bones' (Eph. 5:30). He is not talking about some kind of 'spiritual' and 'invisible' man, 'for a spirit does not have flesh an bones' (Lk. 24:39). No, he is talking of the organism possessed by a real human being, composed of flesh and nerves and bones. It is this which is nourished by the cup which is His Blood, and is fortified by the bread which is His Body. The stem of the vine takes root in the earth and eventually bears fruit, and 'the grain of wheat falls into the earth' (Jn. 12:24), dissolves, rises again, multiplied by the all-containing Spirit of God, and finally after skilled processing, is put to human use. These two then receive the Word of God and become the Eucharist, which is the Body and Blood of Christ.
Source: St. Irenaeus of Lyons, Against Heresies, 180 A.D.:
"The Blood of the Lord, indeed, is twofold. There is His corporeal Blood, by which we are redeemed from corruption; and His spiritual Blood, that with which we are anointed. That is to say, to drink the Blood of Jesus is to share in His immortality. The strength of the Word is the Spirit just as the blood is the strength of the body. Similarly, as wine is blended with water, so is the Spirit with man. The one, the Watered Wine, nourishes in faith, while the other, the Spirit, leads us on to immortality. The union of both, however, - of the drink and of the Word, - is called the Eucharist, a praiseworthy and excellent gift. Those who partake of it in faith are sanctified in body and in soul. By the will of the Father, the divine mixture, man, is mystically united to the Spirit and to the Word.",
-"The Instructor of the Children". [2,2,19,4] ante 202 A.D.,
"The Word is everything to a child: both Father and Mother, both Instructor and Nurse. 'Eat My Flesh,' He says, 'and drink My Blood.' The Lord supplies us with these intimate nutrients. He delivers over His Flesh, and pours out His Blood; and nothing is lacking for the growth of His children. O incredible mystery!",
-"The Instructor of the Children" [1,6,41,3] ante 202 A.D.. ,
St. Cyprian of Carthage
"So too the the sacred meaning of the Pasch lies essentially in the fact, laid down in Exodus, that the lamb - slain as a type of Christ - should be eaten in one single home. God says the words: 'In one house shall it be eaten, ye shall not cast its flesh outside.' The flesh of Christ and the Lord's sacred body cannot be cast outside, nor have believers any other home but the one Church.",
-"The Unity of the Catholic Church". Ch.8, circa 249-258 A.D.,
A lot more early church father writings about he Holy Eucharist:
Early Christians Believed in the Real Presence of Christ in the Eucharist
