From sunrise to sunset, for 30 days, once every year. We call it "Ramadan" and if that doesn't teach you the importance of food and water, then you're cheating at it.
3 days is the longest I've gone with out anything but water when I was16.I never did it intentionally. Besides hungry,I actually felt great, my skin seemed to clear a bit too.
More than once. Busy, forget to eat. Too absorbed and focused on a project and nothing else matters until I realize I'm light headed and thirsty! I also used to fast for religious reasons. So I know the body can go for some time without food. Water is a must though.
Now I keep an almond, walnut, and raisin mixture on top of my desk in a clear covered dish to remind me and give me a snack.