The four venerable sandwich fillings were turkey, tuna fish, cheese and peanut butter. Pamela Durkin, who puts considerable emphasis on health and nutrition in teaching cooking to children, prefers to work with peanut butter or processed cheese if the sandwich will not be made and consumed within a five-hour window. She recommends reserving meat for the evening meal. Cheese offers lots of variety. She also fills a French roll with smoked cheese and a berry preserve of almost any flavor.
Variety appears to be a core concern of many parents.
They would eat it every day. But I use it as a special treat. The combo at Whole Foods comes with 4 pieces each of three different fillings. You make them everywhere with anything. Celebrating the opportunity of making sandwiches in the land of the free, he takes the several elements of the famous salade nicoise and turns them into a nicoise tuna sandwich.