For a 24, you want to sleep in shifts. Have someone rested and able to get in a car if the driver who is out needs to come in unexpectedly. If you are using radio communications, make it clear who is going to be in charge of listening to the pit radio at what time.
If you have the luxury of having a "pit mom/dad" to make sure everyone stays safe and doesn't make stupid decisions, that's a big bonus.
Plan for off-track fuel runs. Who is going to do them and when: the track pumps get crowded and/or run out.
Rag-on-a-stick. Have one or some other plan just in case you need it for your driver to clean the inside of the windshield when it fogs up.
Know that EVEN IF YOU BREAK or are off the track for, say, 8 hours-- YOU ARE STILL GETTING MORE TRACK TIME than you would get if you were entered in a non-24hr Lemons event. So if you all get tired, then STOP. start driving again after everyone is rested.
When the sun is going up / down, the glare is a pain: figure out a way to address it.
The shift where it is pitch black and then the sun starts to rise is a pretty awesome shit to have, according to many.
Some have suggested to put tinting on your rear view mirror to help reduce the glare of the cars coming up behind you with obnoxious led light bars. I swear, those things need to be outlawed on track unless they are mounted on the steering wheel and pointed directly at the driver of the car it is mounted on.
If you don't have a pit steward or dedicated cook who is a non-driver, consider having each team member responsible for buying and preparing 1 meal at a designated time round-the-clock. Helps share the food responsibility. Just make sure not everyone picks Chili as they meal they are going to prepare.