In addition to the above, it may be worth looking at the Didache. It's a fascinating text and a unique window into the early church!
I contend that it's very early, that it was written towards the end of what we can think of as the NT era, so it's very valuable for understanding what the early church believed about God's Word. It's more practical than it is doctrinal, but it contains an Agape-Eucharistic liturgy which, to my knowledge, is the first ever recorded.
I'm quite interested in the Didache, so I'd be glad to expand on any of this, but I can quickly mention that the Eucharist is referred to as "holy" in Didache 9:5, and in Didache 10:3 there's a distinction being made between regular food and drink and what's called "spiritual food and drink" which is connected to "eternal life". And this eternal life is "through Your Servant", which is Jesus (we can know this from the verse above which reads: "Jesus Your Servant").
There are some peculiarities with the liturgy, but it's clearly central to the church of the Didache.