There was a post on Chowhound about this long ago, and I must admit, I am fascinated by "improvisational food." I've been working with the Department of Corrections, and it'd be inappropriate to discuss any current strategies I've heard the folks inside discuss, but I have heard that one recipe that used to be quite popular was crackers crumbled up, placed on thin foil (the kind that might be used for some chips; aluminum foil is usually not allowed: too readily weaponizable), covered with catsup and a layer of American cheese and allowed to sit under ceiling lamps to make "pizza." Then, the lamps were changed out and pizza was off the menu.
This "pizza" could not be much different/better in taste quality than what's being served in the jail cafeteria. But making it gave people some control over what they ate, and I think that sense of control is what may have been most powerfully appealing. If you've ever been in jail, you know what I'm talking about: the loss of control over one's life is probably the most difficult aspect of incarceration.
"Don't you ever underestimate the power of a female." Bootsy Collins