Funny. When I read the title, I thought you meant more of a financial ration than a nutrition ration. I do tend to "ration" the more expensive stuff....my kids are perfectly happy with a sirloin, and I'm not too keen on serving my kids (ages 3 and 6) medium rare meats, so if I'm making a smothered filet mignon topped with gorgonzola, yeah....they get the petite sirloin (much cheaper, but very tasty) cooked to well done. I'll keep the nicer wine for when we have guests, or save my lamb (expensive to us) for special occasions. If it's something expensive (roughy, salmon, etc where we don't live by the water---expensive here), then I serve a little extra of the veggies to make sure we all eat our fill but don't eat every bite of meat in 2 minutes. The water crackers and cheshire or dubliner cheeses are not for after school snacks...if they want some cheese and crackers they can have some pepper jack or cheddar on a few saltines...I like to make appetizers with the nicer cheeses. So yeah, I suppose I do ration some items.
As for what you said though, I'm not preachy at all, but that's just common sense, not financially "thrifty". Don't eat a whole bag of junk. My kids do eat junk occasionally, because I don't really see anything wrong with occasional treats, they are in excellent shape, they are active, blah blah blah. But I mix it up. Like, if the kids sucker me into some mac 'n cheese from the deli, I'll agree.....but then serve it at home with peas or broccoli, fresh tomatoes, and some leftover meat (whatever we have). Can't make a whole meal of junk, so have some of the treat food, but then combine it with some things that will fill her up and be more healthy. Juices: in the morning, the boys have whole milk in their cereal or oatmeal, and a small glass. Then they drink water until lunch time. At lunch, they can have a small juice. Then water until dinner time, when they can have more whole milk. If we go out, it's special and they can have lemonade or sprite, no worries. I'm not a food nazi, but we have to use common sense to teach good habits.
ETA: I do believe that when children hit growth spurts, they start loading up big time...hard to keep even my little ones full when they're about to shoot up an inch or two. When that happens, I will cut out frivolous items and stock up on more milk (our family of 4 goes through 2.5 gallons of whole milk in a week when this happens....we just finished one of those spurts where they both grew 1-2 inches....now we're back down to our normal 1.5 gallons of milk/week), serve more carrots/celery/tomatoes/cucumbers with hummus, more fruits like apples with peanutbutter (if they ask for it) or pears with a slice of mozzarella. It kind of hurts me to hear kids fussy because they're hungry and the mom saying "no", because while they shouldn't snack endlessly on just anything, growing bodies go through periods where they have growing appetites. Just insure that the "extra" they eat is fuel and not dead weight.