The Didache is a very early Christian document, variously dated between AD 50-100; some scholars, such as Milavec, date it between 50-70 [see his book, The Didache: Faith, Hope, and Life of the Earliest Christian Communities, 50-70 C.E] contemporary with the inscripturation of much of the New Testament. It is also a document that gives much insight into the practices and theology of the early Christians.
On the topic of the Eucharist, we read:
Now concerning the Thanksgiving (Eucharist), thus give thanks. First, concerning the cup: We thank thee, our Father, for the holy vine of David thy servant, which thou madest known to us through Jesus thy Servant; to thee be the glory for ever. And concerning the broken bread: We thank thee, our Father, for the life and knowledge which thou madest known to us through Jesus thy Servant; to thee be the glory for ever. Even as this broken bread was scattered over the hills, and was gathered together and became one, so let thy Church be gathered together from the ends of the earth into thy kingdom; for thine is the glory and the power through Jesus Christ forever. But let no one eat or drink of your Thanksgiving (Eucharist), but they who have been baptised into the name of the Lord; for concerning this also the Lord hath said, Give not that which is holy to the dogs. (Didache 9:1-5)
There are a number of important things one finds in the above text.
Firstly, the Eucharist is never understood to be a propitiatory sacrifice wherein Christ is substantially present (Transubstantiation); instead, the Didache understand's the Lord's Supper to be a "Thanksgiving" (Greek: ευχαριστια); indeed, one translation of the Apostolic Fathers renders verse 1 as "the eucharistic thanksgiving" (J.B. Flightfoot, The Apostolic Fathers [1891]). Indeed, the author of the Didache understood the function of the Eucharist was not to propitiate the wrath of God by re-presenting the sacrifice at Calvary, but instead, to serve as an instrumental means to bring about unity of faith ("even as [ωσπερ] this broken bread was scattered over the hills, and was gathered together and became one [εγενετο εν], so [ουτω] let thy Church be gathered together from the ends of the earth into thy kingdom").
This understanding of the Eucharist is found elsewhere in the Didache, such as 10:3, " . . . thou didst freely give spiritual food and drink and life eternal through thy son." To quote on scholar on the Didache:
The congregation thanked God not only for material food and drink, but also for spiritual food and drink: knowledge, faith, immortality, and eternal life. It is not stated in these prayers of thanks that the bread and wine stand for Christ’s body and blood. The Didache therefore did not interpret them as representations of his body and blood, and consequently it does not see the meal as a way of becoming one with Christ. It does, however, regard eating and drinking them as an anticipated, proleptic participation in a future salvation, namely the coming kingdom of God. According to 9:2 the wine represents the vine of king David, God’s servant; according to 9:3 the bread symbolizes the unity of the church gathered into God’s kingdom” (Henk Jan de Jonge, The Community Supper according to Paul and the Didache: Their Affinity and Historical Development, eds. Jan Krans, L. J. Lietaert Peerbolte, Peter-Ben Smit, Arie W. Zwiep, Paul, John, and Apocalyptic Eschatology, [BRILL, 2013], p. 34).
There is no hint whatsoever of (1) the concept of transubstantiation and (2) the Eucharist being a propitiatory sacrifice in the Didache.
Secondly, mirroring historical LDS practice, the Eucharistic prayers are fixed and, unlike most other prayers are not extemporaneous; such a practice is both a rarity in the early Christian community as well as the LDS tradition.
Additionally, in v.5, the qualifications for those who can partake of the Lord's Supper is spelt out. Only those who have been baptised "into" the "name of the Lord," using the same strong positional language one finds in the New Testament, such as Rom 6:1-4, showing that the author understood, as did other patristic authors, that baptism was the instrumental means of initial justification and entering "into" the life and death of Christ (οἱ βαπτισθέντες εἰς ὄνομα κυρίου ["the ones baptised into the name of the Lord"]).
Furthermore, the Christology of the Didache is clearly that of a subordinationist Christology; in vv.2-3, the Eucharistic prayers refers to Christ in subservient terms vis-a-vis the Father, using the phrase Ἰησοῦ τοῦ παιδός σου ("Jesus thy Servant"), with the author asking for the singular person of the Father, not the three persons of the Trinity or the Trinity itself to be glorified, emphasising the subordination between the Father and the Son (σοὶ ἡ δόξα εἰς τοὺς αἰῶνας "to you [sg.] be glory forever").
Finally, just as the version of the Lord's Prayer in the Didache [8:2; cf. 10:5], there is a doxology, mirroring that in Sermon in the Mount; to understand the significance of this, see my blog post here.