The high school I work for has a closed campus, but students still jump the fence when no one is looking (there's an abandoned housing development next to the school, so there's plenty of places to hide). There's really no place to eat off campus that can be reached quickly enough to eat and get back in time for class, unless there are street vendors around -- the nearest market and the nearest restaurant (which is sit-down) are both a couple of blocks away.
The high school I went to in the 90's, which is in the same town but is 10 times the size of the one I now work at, did have an open campus policy for seniors, though I seldom took advantage of it because I didn't have the money to eat out. There are a dozen restaurants, both fast food and sit down, across the street from the school.
I guess it would depend upon the policies of the different schools and where they were located. (The schools I just described are in a smallish town that is part of a large metropolitan area called the Inland Empire, aka IE).
"Oh, you can’t help that," said the Cat: "we’re all mad here. I’m mad. You’re mad."
"How do you know I’m mad?" said Alice.
"You must be," said the Cat, "or you wouldn’t have come here.”
- Lewis Carroll, Alice in Wonderland
| 
