The whistle is because your rescue team may be dropped off a distance away and come to search on foot. If you see that they are friendlies you can blow the whistle to get their attention first without causing surprise. If you come shouting and waving your arms while running out of the trees you may get blown away by the very people that are there to rescue you.

The sunnto compass has a real glass mirror about the size of a credit card built in as a sighting mirror.