What are some good ways to maintain high energy levels during long on-site job interviews?
If you are participating in a 4 to 6 hour interview, you need to realize that that's actually like participating in a full marathon, where you are running 26 miles. You are going to be using a lot of energy. And that means for a couple of days prior to the interview you need to take care of your body to run in that marathon.
Consider eating a carb-heavy meal (your brain actually runs on carbohydrates) and making sure that you get enough sleep. It's critically important that you stay hydrated and have strong electrolytes. So prepare by drinking enough fluids - however, don't chug water right before your interview or else you will have to take a quick trip to the bathroom.
Beyond these body tricks of sleeping well, eating well, and making sure you're hydrated, there are a few things over the course of the day that you could do just to loosen up. When you're making a long drive you often take breaks to just shake it out or something get the blood flowing again. That's a great thing to do during your interivew.
Take a quick break, catch your breath, splash some water on your face, eat a small snack, listen to a short song that keeps you motivated. Remind yourself of a few good points that make you really valuable on the job as a way to just give you a quick surge of confidence over the course of the day that you're interviewing.
Additional Resource: