Backstory: I'm not strict. I'm not a task master. I don't helicopter. I don't spank. I don't yell. I rarely punish, and they are always meant to build, not tear-down.
My kids got a little candy as a desert after dinner when they were small, no sodas. After 5 or so they were allowed a little candy as desert after dinner and lunch. We always stocked big bulk versions of their favorite candies. They got to choose these bulk candies.
I rationed till 6 and then they were allowed to just grab whatever they wanted after a meal, with the understanding that if they consistently went wild with it then I would go back to the job to help them regain control.
They also understood that if they tore through the candy or snuck candy, that was understandable, but we would have to stop getting the bulk candy because too much candy hurts us and we would do what we needed to ensure we are safe and healthy. If control can't be gained with it home, it can be gained once a month at the store by simply not buying it. We would still get candy, but far less often, maybe at a stop for gas or whatever.
They were allowed to eat as much as they ever wanted on special occasions, Halloween, parties, last day of school, vacations, etc. They learned early on how unpleasant it was to go too far with this.
Finally, they were allowed any time to say "I think I want a little candy, can I grab a few (candy type)? And I would make a judgement call based on the days intake and other factors. Surprisingly, they very very rarely used this, even though I mostly always agreed.
Other than having to say "ooh that was a bit much, be more careful next time" sometimes early-on, they became completely hands off with candy and always kept it within reason for their size. If they were unsure, they would ask me to look at what they got. If it was to much, they still got it, always with a "that's ok, next time get less. remember it's not what we do on occasion that matters much, it's what we do every day. So let's make sure we don't do this every day."
I anchored all this to measurable metrics they could understand and see, calories. IDGAF what dessert you eat, you get ~100 calories each meal to spend. That's 6 pieces of gum whenever and however you want them, 6 jolly ranchers, two Oreos, etc.
I essentially mirrored control for them while still letting them have control and a wide choice themselves to exercise within that dynamic.
I knew they would be good when we were at the grocery with my best friend picking up meat for bbq and games all day. When we got to the register he said
"ooh, hey guys get whatever you want" gesturing to the prodigious impulse buy candy display
"We have candy at home"
"But there is so much stuff here. You can get different candy"
"Hmm"
Shocked, I chime in "guys, this is a special occasion, you can eat as much of whatever you want. And, (friend) is paying." Thinking maybe they didn't realize it was a party day, or they were worried about cost.
"Well, we have what we want at home. So, we'll just get some there."
"You can have that too, and get something here. it's a party."
"We're good, but thank you."
He was just, floored. I was beaming. Not because they executed control, they were well into that, but because I knew I had their needs beyond met, and through their lives even when I cease to be able to help them, they would be able to meet their needs better than I ever could.
My oldest is in their 20s. My youngest in their teens. All of them regulate junk of any kind, sugar, media, etc, easily. This is one area I fucking aced as a parent.