i pulled an 11 hour session the other day, with a half hour break for food somewhere in the middle. This was at 25NL though, so i would assume the stamina required for high stakes is different... but if i'm pulling a ridiculously long session i make sure i'm really comfortable, i make sure i'm not at all tired, i have some small snackish food near by ie. some fruit. On that day i also had an energy drink bit by bit as the day passed by to keep me on the ball.

note: that day turned out to be one of my most frustrating poker days ever.. up $4 for 11 hours play.. due to an assortment of bad beats and bad desicions.