Younger children like surprises. Cutting sandwiches into different shapes can be fun. A deep cookie cutter works great for this. Be creative in using different types of bread to put the sandwich on, such as pita pockets, bagels, hoagie or sub rolls. Try a variety of sandwiches, such as using lean meats, cheeses, jellies, and of course peanut butter.
Food coloring can also add some excitement.
Peach yogurt, for example, can be made into just about any color that a child finds exciting, however, use the food color sparingly, as it does not digest and will color the child's stool very interesting colors as well. Children like to handle their food, so pack finger-type foods that can be easily picked up and munched on. Baby carrots and other vegetables are great for this. But so are fruit slices, cheese cubes, and crackers. Avoid chips, as even the lower-fat varieties are pretty much empty calories.