What makes a good 24 hour event? Make sure the players who signed up stay for the ENTIRE game. There are few things that suck more than having your team spanked because 5 guys decided to pack it in and go home.
Make sure that everybody has a tent/basha so they can sleep at the field. It sounds like common sense but this summer at Kelowna's 24-hour milsim, some out-of-towners actually drove back into town and rent a motel. This wouldn't have been a problem except the driver woke up late, took a hot shower etc. and as a result these guys arrived waaay after the game had already started.
But Kelowna put on a kickass milsim this summer. They had generators, lights, porta-potties, shuttle service between the camp and field, large laminated maps at each of the command posts, and well built sandbag bunkers.