In fighting sports, a tomato can is a fighter with low skills who is brought in to pad the record of more promising fighters and give them more ring experience. They are expected to lose. Most professional boxers of any note have dozens of wins in their early careers over tomato cans. The name is believed to come from the fact that tomato cans "leak" red fluid (blood) like a can of tomato sauce.
Philosophical statement made when you put life in perspective, you acknowledge that you are truly blessed, you are truly lucky, and you have all but great things ahead of you.