I know this isn't what you want to hear but I would advise against it. Remaining sedentary for a long time (even if only for a few hours like a normal work day) is not good for you. You sound young so it probably wouldn't affect you much but there is a risk. But excessive caffeine is also dangerous. So if you must, have some general tips:
Change positions or move around often. I would take a 5 to 10 minute break every hour. Use this time to walk around and get your heart rate up. Do some jumping jacks or lunges or something.
Drink water for every caffeine beverage. I would drink at least 2x as much water as caffeine. Also don't just get junk food, go for fruits and vegetables. Not only is it better for you, they give real energy for longer so you won't crash like you will with junk food. That said, go ahead and have some treats too.
Finally, know when to throw in the towel. If you start to get tired and can't keep your eyes open, don't try and push through it. If you start to get a headache or migraine, call it quits. There isn't any glory in a 24 hour gaming session, or a 24 hour "anything" session. I've done gaming sessions or other sessions for longer and it only seems neat that you did it for like a week. After that it doesn't matter.
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