Drinking a glass of wine; a toast, and communion, seals the covenant.

The story of Hamor, mentions three times how they communed to establish the agreement of the bride price.  They also communed with the men of their city to get them to agree to the terms of the marriage agreement.
And Hamor the father of Shechem went out unto Jacob to commune with him Genesis 34:6 .

And Hamor communed with them, saying, The soul of my son Shechem longeth for your daughter: I pray you give her him to wife. Genesis 34:8 

And Hamor and Shechem his son came unto the gate of their city, and communed with the men of their city, saying, Genesis 34:20 

David had a "communion" with the servants of King Saul, prior to marrying his daughter.  At this communion, the bride price of 100 foreskins was established.

And Michal Saul's daughter loved David: and they told Saul, and the thing pleased him. And Saul said, I will give him her, that she may be a snare to him, and that the hand of the Philistines may be against him. Wherefore Saul said to David, Thou shalt this day be my son in law in the one of the twain. And Saul commanded his servants, saying, Commune with David secretly, and say, Behold, the king hath delight in thee, and all his servants love thee: now therefore be the king's son in law. And Saul's servants spoke those words in the ears of David. And David said, Seemed it to you a light thing to be a king's son in law, seeing that I am a poor man, and lightly esteemed? And the servants of Saul told him, saying, On this manner spoke David. And Saul said, Thus shall ye say to David, The king desire not any dowry, but an hundred foreskins of the Philistines, to be avenged of the king's enemies. But Saul thought to make David fall by the hand of the Philistines. 1 Samuel 18-25

David also communed with Abagail before taking her as his wife.

And Abigail came to Nabal; and, behold, he held a feast in his house, like the feast of a king; and Nabal's heart was merry within him, for he was very drunken: wherefore she told him nothing, less or more, until the morning light. But it came to pass in the morning, when the wine was gone out of Nabal, and his wife had told him these things, that his heart died within him, and he became as a stone. And it came to pass about ten days after, that the LORD smote Nabal, that he died. And when David heard that Nabal was dead, he said, Blessed be the LORD, that had pleaded the cause of my reproach from the hand of Nabal, and hath kept his servant from evil: for the LORD hath returned the wickedness of Nabal upon his own head. And David sent and communed with Abigail, to take her to him to wife. 1 Samuel 25:36-38

The word for communion is the Hebrew dabar, which means to speak, promise, say, talk, tell, commune, pronounce, utter, command.
 
And there I will meet with thee, and I will commune with thee from above the mercy seat, from between the two cherubims which are upon the ark of the testimony, of all things which I will give thee in commandment unto the children of Israel. Exodus 25:22 

In Old Testament times, Yahveh would "commune" with the people through the ark of the covenant and the temple.  In New Testament times, our bodies are the temple, and Yahveh "communes" with us directly.   

For I say unto you, I will not any more eat thereof, until it be fulfilled in the kingdom of Yahveh. And he took the cup, and gave thanks, and said, Take this, and divide it among yourselves: For I say unto you, I will not drink of the fruit of the vine, until the kingdom of Yahveh shall come. And he took bread, and gave thanks, and brake it, and gave unto them, saying, This is my body which is given for you: this do in remembrance of me. Likewise also the cup after supper, saying, This cup is the new testament in my blood, which is shed for you. Luke 22:16-20  

For this is my blood of the new testament, which is shed for many for the remission of sins.
But I say unto you, I will not drink henceforth of this fruit of the vine, until that day when I drink it new with you in my Father's kingdom. Matthew 26:28-29

The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? 1 Corinthians 10:16 
 

And they told what things were done in the way, and how he was known of them in breaking of bread. Luke 24:35 

And they continued stedfastly in the apostles' doctrine and fellowship, and in breaking of bread, and in prayers. Acts 2:42 

And they, continuing daily with one accord in the temple, and breaking bread from house to house, did eat their meat with gladness and singleness of heart, Acts 2:46 

And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight. Acts 20:7 

And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God. Genesis 14:18 
 

Today, it is common at weddings to make many toasts with drinking of wine to signify agreement.
 
Yeshua turned water to wine at a wedding as his first miracle.

And the third day there was a marriage in Cana of Galilee; and the mother of Yeshua was there: And both Yeshua was called, and his disciples, to the marriage. And when they wanted wine, the mother of Yeshua said unto him, They have no wine. Yeshua said unto her, Woman, what have I to do with thee? My hour is not yet come. His mother said unto the servants, Whatsoever he saith unto you, do it. And there were set there six waterpots of stone, after the manner of the purifying of the Jews, containing two or three firkins apiece. Yeshua said unto them, Fill the waterpots with water. And they filled them up to the brim. And he said unto them, Draw out now, and bear unto the governor of the feast. And they bare it. When the ruler of the feast had tasted the water that was made wine, and knew not whence it was: (but the servants which drew the water knew;) the governor of the feast called the bridegroom, And said unto him, Every man at the beginning doth set forth good wine; and when men have well drunk, then that which is worse: but thou hast kept the good wine until now. This beginning of miracles did Yeshua in Cana of Galilee, and manifested forth his glory; and his disciples believed on him. John 2:1-11

The interesting thing about this wedding feast is that it took place on the third day.

After two days will he revive us: in the third day he will raise us up, and we shall live in his sight.  Hosea 6:2