We find in 3 Nephi 18 that as part of his temple setting discourse, Jesus first had his disciples administer the sacrament bread and wine to the multitude, and then he spoke to them concerning this ordinance. According to John Welch, although we don't celebrate the sacrament today in our temples, in the Kirtland Temple and in the Nauvoo Temple that was standard. In fact, as a part of the dedicatory service for the Kirtland Temple, after Sidney Rigdon finally got through with his two-and-a-half-hour sermon (Sidney was into long sermons), they broke for the afternoon and came back. Then following the dedicatory prayer and a number of testimonies and speaking in tongues and so on, then the twelve apostles administered the sacrament to all who were present. That was also done in the Nauvoo Temple.
To us the sacrament is a very open thing. Anyone can come and watch us administer to and pass and partake of the sacrament. What we're seeing here [however, is that] when Jesus finally gets to the pinnacle, the last thing that he is going to present to these people is the sacrament, a very sacred inner ordinance. In early Christianity the love feasts, the agape feasts, the eucharistic experience was kept extremely secret. In fact that was one of the things that led to so much speculation about what the early Christians were doing off in these things. People assumed that since they were called "love feasts" they must be R rated or X rated or something. That was part of the reason that the Christians then made the sacrament a more public event in the second century. I point that out simply to say that whatever those [sacramental] prayers were originally, they were kept very sacred and very secret and that explains, I think, to some extent why we don't know exactly what Peter and Paul would have been using as they went around and administered the sacrament to the faithful there. [John W. Welch, "Sacrament Prayers, Implications of the Sermon at the Nephite Temple," in Teachings of the Book of Mormon, Semester 4, pp. 147-148] [See the commentary on Moroni 4, 5]