I did the first 24 hour party (and got the t-shirt). I didn't stay in MK the entire time, I'm not that big of a fan of it, but spent the half of the day in Epcot and AK and from 4pm-6am at MK.
If you use your phone frequently, pack a back up battery (or portable power supply).
Conserve your energy, don't let it all out before the sun goes down. The fun and intrigue occurs in the wee hours of the morning.
Be prepared for housekeeping to wake you up. And Murphy's Law says that the children of your resort will be extra loud the morning after as well.
I have to see how vacation days are flowing around that time. Might as well take advantage of my AP.