According to advice from the Food Standards Agency; 

A healthy packed lunch should include:

• Meat, fish or a dairy source of protein

• Starchy carbohydrate, such as a wholegrain sandwich, to provide energy

• At least one portion each of a fruit and vegetable or salad

• Water or milk to drink, but diluted fruit juice and yoghurt drinks or smoothies are acceptable

The key foods to avoid are:

• Sweets and chocolate. (Magpies will remove bars of chocolate and sweets from lunchboxes and return them to you)

• Snacks, like crisps, with added salt/sugar/fat

• Sugary and fizzy drinks

• Deep-fried foods and processed meats

• White bread - if children won't eat brown, try whole white sliced bread