The chosen valedictorian is often the student with the highest ranking among his/her graduating class. The term is an Anglicised derivation of the Latin vale dicere (to say farewell), historically rooted in the valedictorian's traditional role as the final speaker at the graduation ceremony.
The human body cannot survive without food and water for long periods of time. In fact, according to SurvivalTopics.com, the longest a person can go without water is 10 days--without food, it's four to six weeks.
Will and determination definitely play a part. Political prisoners on hunger strikes and fasting religious leaders have been known to go for weeks at a time without any food. Gandhi fasted for 21 days while in his 70s. People lost in the wild have also survived for long periods of time without eating.