Stayed up for 88 hours during Origins '99
Didn't pound down tons of soda or coffee,
maybe a few cans of diet dew, but I did eat normally.
(That's important, There was one guy at the last gen con in Milwaukee who stayed up the entire con, only on caffeine and energy drinks, collapsed right outside the front door of the con, right after it ended.)
By the end of that period, it felt like my body heat had shut off (felt like I was freezing, and was shivering hard), and I felt like I was piloting myself, like a mech, more than BEING myself.
Oddly enough, I was there just to play battletech.
Mainly stayed up because I didn't have a place to stay, when I got a room for the night friday, I sat down on the couch, and the next thing I knew it was morning.
Then was up for about another 48 for the end of the con and the bus ride back.
I haven't tried anything like that EVER again.