Acts 20:7 (New Living Translation)
On the first day of the week, we gathered with the local believers to share in the Lord's Supper. Paul was preaching to them, and since he was leaving the next day, he kept talking until midnight
Acts 2:42
And they continued stedfastly in the apostles' doctrine and fellowship, and in breaking of bread, and in prayers.
From the First Century AD, before that was even possible, the following was written by Justyn Martyr, born in 100AD, and it describes today's mass perfectly:
On the day we call the day of the sun (ie first day of the week) all who dwell in the city or country gather in the same place.
The memoirs of the apostles and the writings of the prophets are read, as much as time permits.
When the reader has finished, he who presides over those gathered admonishes and challenges them to imitate these beautiful things.
Then we all rise together and offer prayers* for ourselves . . .and for all others, wherever they may be, so that we may be found righteous by our life and actions, and faithful to the commandments, so as to obtain eternal salvation.
When the prayers are concluded we exchange the kiss.
Then someone brings bread and a cup of water and wine mixed together to him who presides over the brethren.
He takes them and offers praise and glory to the Father of the universe, through the name of the Son and of the Holy Spirit and for a considerable time he gives thanks (in Greek: eucharistian) that we have been judged worthy of these gifts.
When he has concluded the prayers and thanksgivings, all present give voice to an acclamation by saying: 'Amen.'
When he who presides has given thanks and the people have responded, those whom we call deacons give to those present the "eucharisted" bread, wine and water and take them to those who are absent.
- St. Justin, Apol. 1, 65-67
G 6,428-429; the text before the asterisk (*) is from chap. 67