An outstanding reflection by Bishop Sheen on The Catholic Thing about why Our Lord chose bread and wine.

An excerpt.

Why did Our Blessed Lord use bread and wine as the elements of this Memorial? First of all, because no two substances in nature better symbolize unity than bread and wine. As bread is made from a multiplicity of grains of wheat, and wine is made from a multiplicity of grapes, so the many who believe are one in Christ. Second, no two substances in nature have to suffer more to become what they are than bread and wine. Wheat has to pass through the rigors of winter, be ground beneath the Calvary of a mill, and then subjected to purging fire before it can become bread. Grapes in their turn must be subjected to the Gethsemane of a wine press and have their life crushed from them to become wine. Thus do they symbolize the Passion and Sufferings of Christ, and the condition of Salvation, for Our Lord said unless we die to ourselves we cannot live in Him. A third reason is that there are no two substances in nature which have more traditionally nourished man than bread and wine. In bringing these elements to the altar, men are equivalently bringing themselves. When bread and wine are taken or consumed, they are changed into man’s body and blood. But when He took bread and wine, He changed them into Himself.

But because Our Lord’s Memorial was not instituted by His disciples but by Him, and because He could not be conquered by death, but would rise again in the newness of life, He willed that as He now looked forward to His redemptive death on the Cross, so all the Christian ages, until the consummation of the world, should look back to the Cross. In order that they would not reenact the Memorial out of whim or fancy, He gave the command to commemorate and announce His redemptive death until He came again! What He asked His Apostles to do was to set forth in the future this Memorial of His Passion, death and Resurrection. What He did looked forward to the Cross; what they did, and which has continued ever since in the Mass, was to look back to His redemptive death. Thus would they, as St. Paul said, “announce the death of the Lord until He came” to judge the world. He broke the bread to set forth the breaking of His own human Body and also to show that He was a Victim by His own free will. He broke it by voluntary surrender, before the executioners would break it by their voluntary cruelty.

When the Apostles and the Church later on would repeat that Memorial, the Christ, who was born of Mary and suffered under Pontius Pilate, would be glorified in heaven. That Holy Thursday Our Lord had given to them not another sacrifice than His unique Redemptive Act on the Cross; but He gave a new manner of Presence. It would not be a new sacrifice, for there is only one; He gave a new presence of that unique sacrifice. In the Last Supper, Our Lord acted independently of His Apostles in presenting His sacrifice under the appearances of bread and wine. After His Resurrection and Ascension and in obedience to the Divine command, Christ would offer His sacrifice to His Heavenly Father through them or depending on them. Whenever that sacrifice of Christ is memorialized in the Church, there is an application to a new moment in time and a new presence in space of the unique sacrifice of Christ Who is now in glory. In obeying His mandate, His followers would be representing in an unbloody manner that which He presented to His Father in the bloody sacrifice of Calvary.

Retrieved April 2, 2015 from http://www.thecatholicthing.org/2015/04/02/bread-and-wine/