In the chapter titled "I Find Many Useful Plants" in Jean George's young reader's novel My Side of the Mountain, Sam Gribley begins exploring his great-grandfather's farm that Miss Turner, the librarian, had marked on a map. He discovers a stream that would benefit him more easily than the big mountain creek for fresh water and fish. He also sees that Miss Turner's prediction had been correct--the old farm house was nothing but ruins. All he finds are "a few stones in a square, a slight depression for the basement, and trees growing right up through what had once been the living room" (p. 27). After discovering apple and walnut trees, he turns to further exploring the foundations of the house, "hoping to uncover some old iron implements that [he] could use" (p. 27). However, he further says that he was unable to find any because "too many leaves had fallen and turned to loam," meaning rich soil, and "too many plants had grown up and died," covering up the site of the old farm house. He decided he needed a shovel to carefully search through the soil for old iron implements and would come back when he had made himself one.
While we are not told exactly what he hopes to be able to use the iron implements for, it can be assumed he was hoping to be able to use them to make tools. It was during the Iron Age that the ancients began using iron implements rather than bronze or stone implements to make tools and weapons, which significantly changed history since iron is the strongest metal. The Iron Age began at different times for different civilizations but can be traced back as starting in at least 1200 BC in the Ancient Near East.
Hence, as a well-read, intelligent young person, especially one well-read in survival, Sam would have known the benefits of using iron implements to make tools; he would also be smart enough to know when a shovel would come in handy.