One of the things that I used to make sure I'd do was to always make sure I'd have dinner at home because I needed that disconnect from work. Even when it was crazy, I'd go home at, like, 10 o'clock and have dinner. That way, I had time where I could decompress a little bit and then go back in.
Don't eat the pizza; get lots of sleep - you have to take care of yourself. It's about being your tip top self at all times, and if you are unhealthy, or you're sick, or you don't feel good, even it's just because you're sluggish, you're not going to make it because you're not going to be able to react to things.
You're following your track, the story, your only plan, your map for the audience, and all the other stuff is, like, the fun stuff: the costumes, the locations, the set-dressing and the actors. They can all be variable as you like if you stick - however roughly - to the path.