I think the question is: What is the food and water that Jesus went without for 40 days and 40 nights?
John recorded Jesus as saying:
“I am the bread of life. Whoever comes to me will never go hungry, and whoever believes in me will never be thirsty." (6:35)
and, "Jesus said to them, “Very truly I tell you, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you." (6:53)
God spoke through Jeremiah and said:
“My people have committed two sins: They have forsaken me, the spring of living water, and have dug their own cisterns, broken cisterns that cannot hold water. (2:13)
John recorded Jesus as saying:
Whoever believes in me, as Scripture has said, rivers of living water will flow from within them.” (7:38)
And Isaiah prophesied:
People of Zion, who live in Jerusalem, you will weep no more. How gracious he will be when you cry for help! As soon as he hears, he will answer you. Although the Lord gives you the bread of adversity and the water of affliction, your teachers will be hidden no more; with your own eyes you will see them. (30:19, 20)
This is a fraction of Scriptural references mentioning food and water. John describes more about this, as do the prophets, but I hope my observation is clear. Many people think of food and water in purely physical terms, but clearly there is more to food and water as described in Scripture than apples and, well, water.
To answer your question, I think that Jesus set his deity aside and ventured into the world of man for a period of time, 40 days and 40 nights, and tried to rely on his own understanding of Scripture to continue his course as God's salvation for mankind. As the Son of God he had limitless power to live, but as a man he was weak and experienced our weaknesses as we are being tempted and succumbing to temptations of the flesh. Jesus did not succumb to the temptations.
Jesus had to do this so that we could be able to relate to him, AND so that we can call on him to help us in our times of weakness.