What can the school do if I don't choose to follow their requests? Isn't it our choice as parents to give our kids what we want them to eat?
If the school was specifying one brand of this and one brand of that and requiring that the children only have that specific thing for lunches, I would say you are not being unreasonable for asking this.
But that's not what they're specifying, and you are being unreasonable. They are likely under pressure from the government and local authorities to implement healthy eating initiatives. I know in this country, childhood obesity is on the rise and myriad illnesses, many of them long term and life-limiting, (or at least quality-of-life-limiting), stem from obesity which can be linked to poor nutritional choices. Not only that, but multiple studies have been conducted that have concluded there is a quantifiable link between nutritional choices and academic performance: put simply, children who eat crap, tend to give crap performances academically. Children whose parents make good nutritional choices for them tend to outperform those whose parents don't.
To sum up: the healthy eating initiative is a) to boost your child's health, b) to boost your child's academic performance, and c) may well be due to pressure from outside authorities.
But you're right. You're the parent. How very dare the school be concerned about your child's physical, intellectual, and emotional well being?
Succinctly, YABU. If you want to fill your child with sugary processed crap, do it on your own time.