My kids never ordered food on their own. When the family ordered, we were fairly open to letting them have extras (apps, dessert, soup/salad, etc.), but it wasn’t a weekly occurrence and we would have let them know if they were going crazy.
For snacks, there was plenty of stuff at home that they could help themself to. If they wanted something specific, they were welcome to add it to the grocery list, and most likely it would be picked up on the next grocery run.
Their money was their own. If they had wanted to spend their money on chicken wings, I might have had one brief talk with them about it, but I would have let them proceed. It wasn’t, however, an issue for us.