When he crashed on the Island, Sawyer was a self-interested opportunist. He spent a lot of energy collecting a sizeable stash of items. He carefully guarded these items, and leveraged them to get what he wanted from the other survivors throughout their time on the Island. Sawyer showed some humanity at times, and gave items to the others without exchange, such as the heroin to help Libby with her pain. This is how Kate was able to see the location of the stash, which turned out to be buried in Sawyer's tent, under a sign that was covered with dirt and a tarp. ("?")