No mobile ecosystem would be complete without a bevy of flashlight apps (just beware which flashlight app you download). And the Windows Phone store is no different. And one of the most popular for WP has been Flashlight-X.
The app offers up a number of useful tools including a continual light source from the phone's flash, a blinking SOS mode for emergencies, and a decent compass that works even when you are out of range from your network signal.
Even if you don't use this app on a daily basis, it's a useful tile to have pinned to your home screen should an emergency arise—or for when you need to make your way around when the lights go out.