geewhiz . . . too bad your son is not old enough to purchase his own food choices while visiting his father.

i think you should purchase foods your son wants and allow him to bring it with him on trips to see his father. his father should respect this arrangement. tell your son to call you if he isn't allowed to eat his food he brought with him. hopefully, it doesn't resort to this. it would be nice if you could prepare a list of foods for the father to purchase and have ready for his son.