I have doing that multiple times, this is my advice
1.Sleep more 2 days before the event (you can do exercice or other stuff to do that)
2.Don't drink coffee or any sugar base beverage for the week before this, the day of the event you can drink anything and get improvement in resistance
3.Take breaks yeah ,you need take breaks to be in the better form to play, try the 5 minutes between change maps and the end of round 1.
4.Eat enough, its important to be alert
5. This is the most important, put a sticky note front of you to remember what are you doing (yeah sounds crazy but can save you in the last hours)
6.Check your posture, if you play for that long, your back will hurt...
Heal advice
be awake more than 30 hours can be dangerous so be careful with this, first don't drink a lot of shit like coffe (can affect your heartrate), second don't be sitting for the 24 hours; the blood in your legs can accumulate and provoque a stroke or a heartattack (its not a joke). Third be aware of your state, if you feel dizzy or with headache probably its time to stop.
Take care and enjoy the event..
sorry if i have errors in the text