Why did Jesus, the all-knowing Son of God, choose grape wine and wheat bread for the Eucharist? I will give my opinion here, which, in so far as it might be correct or partially correct, is certainly not the whole reason.
1. Jesus knew that wheat bread and grape wine would always be available to the human race for as long as the Eucharist is needed in the future.
Wine is popular enough among the wealthy for its taste and similar qualities, so that their wealth will always make certain that vineyards stay in business. Wine is popular among people more generally because it has the properties of inebriation (hopefully only minimally) and is used in cooking or goes well with meals. Wine is popular for celebrations. Thus, grape wine will never pass away from widespread availability among humanity.
Wheat has the properties of gluten, which allows the bread to rise well, unlike other staple foods. It was long considered the food of the wealthy, so it is protected by wealth. It has the property of rising well with yeast (leaven), which gives it a structure and taste fairly unique among grains, and for which there is no easy substitute. It is popular in taste around the world. Thus, wheat bread will never pass away from widespread availability among humanity.
Jesus chose foods that would always be with us, so that He could always be with us via the Eucharist.
Also, both wine and bread have a property where simple foods are transformed by yeast — grapes ferment to produce wine; wheat flour rises by the action of yeast — from one food into another. This is analogous to a human being being transformed by grace and by the teachings of Christ into a better person, a person renewed by Christ.
Also, bread works well as a symbol of the body of Christ, and wine world well as a symbol of the blood of Christ. Yes, I know that the Eucharist is no mere symbol, but is truly the body, blood, soul, and divinity of Christ. However, it is also symbolic that this presence in the Eucharist is separated into a blood-like wine and a body-like bread.
Food for thought.
Ronald L Conte Jr
the reproach of Christ 
While wheat and grapes may be the most widespread and common alternatives, I am sure they are not absolute. I would expect places like, say, Greenland to be bereft of them for at least temporary periods. How did the Church deal with such situations before we had worldwide air transport?
The popularity of wine and its ease of manufacture mean it will be available even where there are no grapes, and the same of wheat bread. Even leavened bread is valid matter, and all you need to make unleavened bread is flour and water.