Every emergency survival kit should include various methods of signaling to draw the attention of rescuers.
Whistles are an audible source of notifiction that can be used when others are likely within ear shot to draw attention - such as when the search lights of a ground team can be seen in the area. These are best used in locations where sound can carry and not echo all over the place, so the source can easily be located by search teams.
Mirrors are a visible signal that can be used to draw attention of someone within sight - reflecting the sun light to create a beam to shine in front of a search team so they can follow it to your location. These are best used in high vision locations with sun exposure to allow spotting search teams and ease of signaling.
Signal Panels are typicaly orange or yellow sheets that can be waved in the air, stretched out in an open area or used as a shelter entrance so a passing search team can spot it. These are best used in highly visible locations where a large area will have line of sight to the location.