What school is this? Because when my child was in primary school they would inspect every child's packed lunch. Anything that didn't meet their standard would be handed to the student with a warning not to eat the forbidden item (usually something that had too much sugar). He would then get told to "tell mom and dad" not to pack that item in the lunch again. Mind you they never would tell the parents what was approved or not, there was no list or even any guidelines. (And to be clear I'm not talking about peanuts or other potential allergy issues, just sugar content or types of foods that felt were not appropriate).

I have zero doubts that an empty lunch box would have seen the parents of the child reported to the local authority.

(Child no longer attends this school.)