I am regularly asked what I give my kids for lunch going to school. The answer is real food without the grains when possible.
So a combination of a good protein source like good quality ham, hard boiled egg or greek yoghurt with seeds added, a good healthy fat source like cheddar cheese or olives and some low carb veggies, like cucumber, and cherry tomatoes. There are so many options its really a case of mixing it up to see what they like. I ask them the night before what they would like and they choose.
They really enjoy this food and it definitely helps with their concentration. Any by the way no juices, whole milk of water are the best options.
So get plan to get rid of the sliced pan, cheese strings and super sweetened yoghurt sticks. Food for thought!