Just eat what you normally eat. Obviously if you're eating pizza/burgers on a regular basis, you should probably opt for a lighter meal + change what you normally eat as well.
Also try to opt for the safer side of things. If you normally drink OJ for breakfast, perhaps try water instead. I had an experience when I usually have OJ, but that morning along with anxiety from having a big test, I had massive stomach pain throughout the process. No seafood, weird meats, processed foods, street food, etc.