I took part in Sarcastic Gamer's ExtraLife charity, 24 hours of gaming. I was fueled by Turkey sandwiches and tea in the early going, then Pizza Rolls and Red Bull towards the end.
My longest non-charity gaming marathons would probably be about 8 hours long. I'm not sure if that would be WoW, Oblivion, or some RPGs from my past when I had more free time. Fueled by lots of Pizza Rolls and Vault / Surge.
About 8 hours or so playing games online with friends is usually the most I can handle. The only time I've played a whole (long-ish) game all the way through was when I beat Ratchet:Deadlocked co-op with my brother, but even that was only about 6 PM to 2:30 AM if I remember correctly.
I have been on "game nights" a few times so 15 hours none stop...
Also Dragon Age Origins - 10 days straight, 10 hours each day. Dragon Age 2 - 5 days straight, 12 hours each day. Food? Hmm... dunno the usual stuff... although I don't feel hunger when I'm playing games...
P.S. - I'm european so I'm skinny :)
Mass Effect 2, the only game I ever stayed up all night to keep playing, started around 7ish pm and I can't remember when I stopped, but I defenitely went into the afternoon. Only break I took was at 8 in the morning for about 15 minutes to walk the dog. Only reason I did it was because I had to walk the dog in the morning, and I didn't think I'd be able to wake up early enough to walk him at the proper time.
When I was in high school I played Morrowind for over 24 hours straight (obviously excluding bathroom or beverage breaks) once when I was sick. I forget exactly how it happened, but when I went to save, the power went off for a second or maybe the game just froze as it was prone to do, and I lost all my progress. I didn't touch the game again for several months.
My first Persona 4 experience was 8 hours long; Dragon Age 2 has been 5 hours nightly for the past week; MW2 was a 9PM-2AM deal every night when it came out for about 3 weeks.
All of these sessions were fueled with green tea and clementines/watermelon. I can't down caffeine; it literally puts me to sleep faster.
When I was a kid my neighbor and I would have 'sleepovers' where we just stayed up all night playing video games. We'd start at six or seven the night before and play until noon the next day or so. Rock n' Roll Racing, Killer Instinct, Street Fighter 2 Turbo, Secret of Mana, etc. Many Mountain Dews and bags of popcorn were had. Good times.
Gotta be the second banjo game. I mean, my goodness, I literally played that as a kid NON-STOP. and I don't joke about that, about a week strait with no breaks other then sleep, dinner(sometimes.) lunch. awesome videogame. bad thing though, my eyes got so sensitive to light that once our countie fair came up with some crazy Xboxdome thing with a bunch of videogames being showcased in it, I was unable to play any of the games without my eyes feeling like they bug outta my skull.
I only regret not being able to play that Godzilla fighting game there.
In high school, I would frequently spend the entirety of my weekend playing WoW. Come home from school on Friday, play till 3 am, maybe sleep for 3-4 hours, wake up and play all day Saturday, then do the same for Sunday. Of course, I would always stop for food and bathroom breaks. I'm glad that part of my life is over though, it's nice to get out of the house on the weekends, see friends and such. Most recently though, I I spent 7hrs playing Fable III straight, only to have it glitch out on me. If I want to play it again, I'd have to restart, I'll pass for now :)
A friend and I played 36 hours of Resident Evil 5 when it launched. We beat the game once, then maxed out every weapon till infinite ammo, finally we beat the game on professional. Crashed hard after that. Although I can't pick out any instance, I'm almost certain I had close to the same stint back in Diablo 2, I spent a lot of time in trade chat.