It does sound like a problem. I still suggest asking the teacher about where the students are supposed to put their lunchboxes. If you know what the routine is, then you will know what to suggest in that note. The trick here is making is easy to remember.

Yes.. I agree open drinks should get thrown out. But bringing home all the leftovers made me more aware what my kids were really eating. We really only did that in the early grades.

Good Luck.