Sadly, I think this what has become the "norm" in many schools today. As a kindergarten teacher myself, I see the poorest food choices everyday. Food and eating is a learned behavior.... So with that said, you can instill in your child what others aren't installing in theirs.
As far as lunch choices in schools go... Ugh don't get me started. Yes, schools are offering healthier choices and limiting their snacks, but there are still many kinks to work out.
You should pat yourself on the back for being such an aware parent who is in-tune with health and nutrition