One survival tool that does not get enough credit is a good whistle. When attached to your pack or keys, a simple whistle can save your life in an emergency situation. This is because of the fact that the shrill sound they produce will get more attention than a voice. If you are stranded in a survival situation, you can use a whistle to send an SOS much farther than your calls for help will carry. They also have utility beyond survival, such as serving as a long range way to signal that dinner is ready or that you are headed back to camp.