Dealing with Best Friend's Death?

My best friend whom I have known since I was 5 years old passed away at the age of 53 this week with melanoma cancer. The disease was found in the later stages and death was inevitable. For three years I watched as my friend's health slowly decline and it hurt because all I could do was stand by and watch. We went to the same grade school, high school, and we were both in the same college fraternity. My friend had many friends and was very popular. He was very successful and was always so happy, whether he was traveling all over the globe with his wife and two kids (5th and 2nd graders) or out partying with his friends. He always had a smile on his face. The realization of his death is still sinking in. I have been asked to give a 5-7 minute speech at his funeral tomorrow. I hope that I have the strength to prevent myself from breaking down in front of everyone. I don't know how to handle this situation because I have never lost anyone close to me until now. Although I have many friends, I had no truer and closer friend to me than him. No one, other than my wife, knew me better than him. I just can't believe I never will get another chance to speak to him again or see him with a smile on his face. How should I handle this situation?