48 hours... on a schoolvacation with the entire class to Austria. I couldn't sleep in the bus. So I stayed up... without coffee or any stimulant, mind you.
When I finally got to the destination I laid on the bed and slept like a log for 12 hours. They even threw water in my face to try to wake me for dinner, but I just wouldn't wake up.
And 48 hours another time before my first high school senior year exam. I'd just tried out coffee plus the effect of nervousness kept me up all night. I aced the exam though.