Sorry - I haven't read the whole thread, so apologies if I'm repeating things. My DS had packed lunch for 3 years, his school didn't issue any guidelines apart from no nuts but if they had said something like no crisps or no chocolate it would have annoyed me. My DS was premature and still underweight so I was constantly trying to find nutritional but high calorie things to feed him! ie in many ways the oppostite of what you would would feed a child who was overweight. That's why I don't think you can really dictate rules. There are also realistically some days where a sandwich, garb a bag of crisps, chuck in an apple and a KitKat is all you have time for 
However it is BORING making packed lunches everyday so it is really useful to have some ideas from other people. Some days he had baked beans or chunky veg soup/stew in a small thermos, cornish pasty, sausage rolls (but if he had that he would also have carrot and red pepper sticks for example as well as fruit) often things that were left over from supper so a salad with brown rice, roast veg and cheese, chicken drumsticks, hard boiled eggs, scotch eggs, slice of quiche, anything in a 'wrap' to make a change from sandwiches. Also people could freeze different types of bread roll so there is some variety.
"puddings" that worked well were flapjack, malt loaf, homemade cake, rice pudding pots, custard pots.
What about a recipe book? Maybe the children could post their suggestions of what their favourite lunches are? I think it would be most helpful for people to see an overview of a good lunch box rather than just individual items. Also some people seemed to think they were feeding King Kong judging by the portion sizes!