If I were stranded on a desert island, I would take with me a flint-stone and a knife.  I would use the flint-stone to create fire.  I can use the fire to keep warm, boil water, cook raw meat, and scare away predators.  I would bring a knife to kill my prey including fish and other animals for food and protection.  A knife is also useful for building things like breaking off branches and leaves of trees to make a shelter.