Food is definitely on the list of items you can’t take in.
I’m doing this trip on a thin shoestring, so I’m making plans for how to avoid buying food any more than I can help. I’ll have a cooler in my car, and I plan to have a “car meal” in the car after parking and before getting out to head for the entrance. My goal for the trip is to only actually purchase one meal a day and eat the rest from what I have along with me.