Why did Brian think he could never again throw anything away?

The question is from the story Hatchet by Gary Paulsen.

Brian is a young boy who finds himself all alone in forest. He had to survive from the things he could made which include bow and arrow to catch fish which serves as sources of food. He had no hope of how to come out of the forest because the people who came to get him turned back after getting very close to where he was hidden away from the sound of the plane. He felt hopeless for returning home but he finds new hope in his survival and ability to hunt and get himself food to eat.

His experience in the jungle made him think he could never throw anything away because anything can be useful up to his shoe lace that he used in making his bow.