You sleep when you can where you can same goes for eating.
as ViR said wood>tent>car
some games will cut out for a few hours where everyone returns to their base and camps it for the night, others will run the full 24hrs so you have to set up a patrol and guard while others sleep.
The only time I can see a car being acceptable during a 24hr event is in case of injury or there is a vehicle in game.
some people push themselves through the full 24 hrs.
others dont make it past hour 10.
Most team leaders have mandatory rest periods in which squads rotate through the CP to catch a few winks or some food.
A lot of guys pack snack foods and MREs to munch on during play, while moving out you can always eat a granola bar.
"You know what the chain of command is? It's the chain I go get and beat you with 'til ya understand who's in ruttin' command here."