Currently, the only time I play for what would be considered a really long time are either: a) Gen Con, where I can sometimes end up GMing three Pathfinder Society scenarios in one day which adds up to about 14-15 hours of play; or b) Extra Life, when I game for 24 hours straight.
But back in junior high, my pals and I would get together for our weekend-long sessions of D&D, hosted at one of our houses. Friday after school we’d pack our games, dice, and obnoxious amounts of junk food over to whichever home had accepted the Horde that weekend. And we would play RPGs until the parents got sick of us and sent us home Sunday afternoon. Usually we’d blast through whatever the latest AD&D module was (the weekend we played G-1-2-3 Against the Giants still lives as one of my favourite memories), but these weekends were also when we’d take a break and try out other games: Paranoia, Skyrealms of Jorune, Car Wars, GURPS; we ran the gamut.
These days, of course, carving out that kind of time for gaming is well-nigh impossible. But I like to think that maybe, someday, we’ll manage to ave one of those weekends again.