The term 'CAMPSITE RESIDUE' can be broken down into two crossword solutions: ASH (3 letters) and ASHES (5 letters). ASH is a light-colored powdery residue that is left behind after the combustion of organic material, such as wood. ASHES are the solid remains of a fire, which are usually composed of charred wood, minerals, and other materials. Both ASH and ASHES are common residues found at campsites, where campers often build fires for warmth and cooking.