This is where the 'freezing a plastic water bottle' debate comes up. I am not a fan of constantly freezing plastic bottles as the freezing and defrosting may break down the plastic which leeches into the water, which is then ingested, blah blah... Doesn't matter whether it is a Mt Franklin type bottle or a BPA free bottles, plastic - cheap every day type plastics - are not designed to be frequently refilled and reused or exposed to extreme temperature.
Stainless steel is a better option, in my opinion, for sustainability and longevity, BUT it has the disadvantage of not being able to be frozen. With the wide necked bottles like the ECOtanka you can add ice cubes. Lots and lots of ice-cubes!
Back to the lunch topic...
We are lucky at our school, all the children get a lunch provided each day in a dining hall. It is usually something hot, it is vegetarian and each serve has a serve of veges in it, even mac and cheese... The things the cook can do to sneak veges in is amazing! The children also have a plate of fruit, bread and spread condiments for sandwiches, a container of grated cheese, a jug of water and a container of sultana's. One of the most popular sandwich combo's with the kids is honey and sultana!