S.P.
You did not mention his age but here are some suggestions.
Macaroni and cheese
Grilled cheese
Soup or ramen noodles with leftover meat/frozen mixed veggies
crackers with cheese and a little mustard on top, or with any cheese spread or chopped leftover chicken with a little mayo mixed in
mix baked beans with cooked rice
nachos
quesadillas
cut-up raw veggies and ranch dressing (dip)
Pita bread with filling
Pita bread or tortilla pizza
Apple slices with peanut butter or soy butter
egg/cheese sandwich
sliced hard-boiled egg sandwich with mayo
egg salad filling for any of the above(on crackers, with pita etc.
Hope this helps.