How do I survive 4 interviews in one day?

Why would you do that to yourself? 

My first piece of advice is to see whether you can swap/reschedule any one of those. Not gonna lie, that's a monster day and your performance will likely suffer as you get fatigued.

If you REALLY can't avoid it, endurance is key as you need to sustain yourself throughout the day. I've done a 4/5 hour super-day before, and I literally felt like I was going to fall asleep during my last interview. Anyways, here is what I would recommend 

1. Proper nutrition, especially in the morning, focusing on complex carbs (think oatmeal/wheat bread etc) for sustained energy. Avoid sugar bombs like candy, etc. If you need a quick fix, have some fruit instead, much more nutritious and you feel better after. Avoid heavy, high sodium/fat things as well, I feel like that will put you to sleep. 

2. Have water, Gatorade handy and a quick snack like a granola bar handy. You can snack on that between interviews.

3. If you have the time, take a nap between them? Even a 30 minute one may help, but don't wake up too close to the interview or you will feel groggy.