So here's Justin on the Eucharist, first from chapter 65, Administration of the Sacraments:
But we, after we have thus washed him who has been convinced and has assented to our teaching, bring him to the place where those who are called brethren are assembled, in order that we may offer hearty prayers in common for ourselves and for the baptized [illuminated] person, and for all others in every place, that we may be counted worthy, now that we have learned the truth, by our works also to be found good citizens and keepers of the commandments, so that we may be saved with an everlasting salvation. Having ended the prayers, we salute one another with a kiss. There is then brought to the president of the brethren bread and a cup of wine mixed with water; and he taking them, gives praise and glory to the Father of the universe, through the name of the Son and of the Holy Ghost, and offers thanks at considerable length for our being counted worthy to receive these things at His hands. And when he has concluded the prayers and thanksgivings, all the people present express their assent by saying Amen. This word Amen answers in the Hebrew language to ge'noito [so be it]. And when the president has given thanks, and all the people have expressed their assent, those who are called by us deacons give to each of those present to partake of the bread and wine mixed with water over which the thanksgiving was pronounced, and to those who are absent they carry away a portion.
(1) It's worth noting that the Kiss of Peace isn't some new invention of the American Church to make everybody feel wonderful inside: it's a long-standing Catholic tradition.
(2) The Eucharist is only open to the Baptized individual "who has been convinced and has assented to our teaching."
(3) The Eucharist consists of bread and wine, mixed with a bit of water. This is a practice done (to my knowledge) only in the Catholic and Eastern Orthodox churches.
(4) The Eucharist is brought to the absent. This seems like a minor detail, but it invalidates the Lutheran Church's Eucharistic views, where the blessed bread and wine are incarnated in some sense with Christ during the duration of the service, and not afterwards.
(5) All of this very much mirrors the modern Mass: Prayers of the Faithful, the Sign of Peace, the Eucharistic prayers over the bread and wine mixed with water, and the Great Amen.
(6) However, Justin says "deacons give to each of those present to partake of the bread and wine mixed with water over which the thanksgiving was pronounced." At first, this sounds like he's denying the Real Presence. But then you get into the nitty-gritty of the Greek, where thanksgiving means Eucharist. So he's literally saying "deacons give to each of those present to partake of the 'Eucharitized' bread and wine mixed with water."
He makes it more clear in the next chapter, which picks up immediately where that last quote left off:
And this food is called among us Eucharistia [the Eucharist], of which no one is allowed to partake but the man who believes that the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh.So Justin is clear "that the food which is blessed by the prayer of His word [...] is the flesh and blood of that Jesus who was made flesh. " The "prayer of His word" refers to the words of institution, which come from Jesus' lips at the Last Supper. So after the words of institution, the bread and wine become the flesh and blood of "that Jesus." The phrase "from which our blood and flesh by transmutation are nourished" is sometimes rendered, "in order to nourish and transform our flesh and blood," and the Greek here (kata metabolen) means something very similar to "metabolize." So just as with physical food, it becomes part of our bodies, through the spiritual food of the Eucharist, we become part of Christ's. We eat Him, but rather than us metabolizing Him, He "metabolizes" us.
(First Apology, 66)
I really enjoy this part of the First Apology not just because it's fascinating how constant the Mass has remained over the last two millenia, but because I really like Justin's insight into the Eucharist, and the idea of Christ "metabolizing" us.