First, a bit of education:
Whole-Grain breads are the best for you in nutrient content because of the fact that the whole grain has been used in the making of the bread and certain nutrients have not been processed out. To learn more...
With that info in mind, try this sack lunch menu for your child's lunch at school:
Multi-grain bread with 2 tablespoons of peanut butter (or almond butter) and 1 teaspoon of raspberry or grape jam, melon wedge and 1 cup low-fat yogurt.
A tip: Most grocery stores carry low-sugar or sugar-free jam. Give that a try to cut down on the sugar.