I'm curious about how food/rationing works onboard the Enterprise. We know that there are food synthesizers in multiple locations that can make anything you want, and if I remember correctly, will take verbal requests. We also know that at least Kirk has medical oversight of his diet - a yeoman brought him salad after McCoy "adjusted his diet card", with the obvious implication that Kirk was not allowed to go get something else from the synthesizer.
So...how much dietary regulation are crew members subject to, and how is it enforced? Are you issued specific food cards ahead of time to use in the synthesizers (like Chapel used to get the kids all the different ice cream flavors)? That would seem to take the joy and free will away from having a universal food synthesizer. Since only raw matter is needed to produce food, I imagine rationing isn't logistically necessary, but maybe it's needed to keep crew members fit. But then we see that some crew members have alcohol or other treats in their quarters (Scotty's impressive liquor collection, for one), and how would Kirk gain weight if everything he ate was strictly controlled? That can't be right.
Any theories? We never see a fat crew member during all five years of the mission, so they must be doing something right. :P