I must say, I question that it would actually work. If children are going to eat out of school, then stocking healthier options at the shops would be pointless, as most are not going to choose them anyway, over chocolate and crisps. While we may kid ourselves that by giving children the option to eat healthier items (which I think most shops do, at least, try to nowadays), they will become healthier, it is just not the case. They will more often than not choose what they like and what they are used to, not what is good for them.
If you want children to eat more fresh fruit and vegetables in school, then you have to give it to them freely. I know in Primary schools, fruit is given daily, but this has to be carried through into secondary education, otherwise the temptation of the sweet shop or chippy is just too much.
Ian