Yep, been there.
Nothing like a 6 year-old opening up lunch bag to find a container of plain tuna or cottage cheese and an apple. Makes you real popular among the kids who trade lunches. At one point getting some pineapple in with the cottage cheese was a treat.
Not really diet, but "healthy" – instead of cookies or snack cakes my Mom would give me about two tablespoons of raisins and peanuts mixed and tied up in a piece of plastic wrap. Another was two ginger snaps sandwiching a piece of sharp cheddar. Yeah, I was a real popular kid. [;)]
Of course, we drank gallons of diet drinks. Tab was the standard, but Fresca was pretty popular, too. We also had a 5 pound bag of cyclamate "sugar" that my Mom held on to for years. In the summer I’d make really awful iced tea with it.