Spruce sap also makes a great natural firestarter. The flammable substance oozes out of injured trees and hardens into a resin, which can be snapped off and set ablaze. Still, Aherns warns that it may take several matches to get it going. Once lit, though, the sap will burn for several minutes, making it a great resource in wet conditions. While spruce is best, any hardened sap will do. Just find a blob that’s about the size of a wad of chewing gum, pull it off the tree, place it on the end of a stick, and light it up.