If you're planning on living in the wilderness until whatever happened had resolved itself, a flashlight is not the most useful tool.
However, having one can be very convenient, as well as a stress-reducer, especially on your first nights out, before you get your bearings and set up
camp. There are other situations too, where a flashlight is much preferable to a fire or similar large light source. Evading pursuers, for example,
you're not going to want to light up a visible fire, and you may not have the time or inclination or ability to build a fire hole, but you may need
light for cleaning your weapon or rigging a line or setting snares, or whatever. Throw a hood over your head and you can see perfectly to do whatever
small task you need to do, without putting up a bat signal.
If you're going to bring a flashlight (and I do think it's a good idea), it might be better to pack one small emergency light, batteried and bulbed
and ready to shine, and another flashlight without bulb or batteries - instead pack some tackle in the cavity and keep the batteries in their original
packaging, along with a couple of bulbs in a watertight case.
If something breaks and you're in the forest, try to find alternate uses for the component parts. Where else are you going to find machined metal
tubes and reflective disks in the wilderness? This instinct came naturally to our forefathers, but it has been dulled somewhat, I think, by constant,
racheted-up exposure to disposable consumer culture.
Flashlights can still be useful, even without a bulb. I'm a smoker, so my BOB's gotta have a couple of cartons of smokes. A nifty trick I picked
up from the Search and Rescue bible is that you can light cigarettes with the reflector from a flashlight, and of course cigarettes can be used to
kill cravings and ignite tinder at the same time.
Also, on that note, people should not neglect the psychological aspect of survival. I've seen a lot of information (good information) on this
thread, pertaining to tools and tactics, but little in the way of mental preparation, which is by far the most important aspect IMO.
For example, knowing the ins and outs of survival fishing and trapping, and having a pack full of gear designed for that purpose, is useless if you
spend the whole day crying underneath a tree because you miss your family and you're hungry and tired and afraid.
The will to survive is really an amazing thing, I've seen it, I've felt it firsthand, it's awe-inspiring. But all too often panic sets in, and
people wind up crippling themselves mentally. Once when I was backpacking, one of my cheap synthetic hiking boots came apart in a stream. I was two
days from my destination, and it had been a miserable experience from the start. We had an injured person already, and I was very close to just
sitting down on a rock and waiting for someone who gave a damn to come find me. Mentally, I was very close to my breaking point.
As survival situations go, losing your shoes is not that
bad. Or rather, it could be a lot worse, it can always be a lot, lot worse. Those
are the sort of thoughts that get you off the rocks and back on the path...
One good technique I know of is using familiar habits and things like comfort food to mitigate the effects of stress. Something as simple as crackers
and peanut butter, or a candy bar, or a cigarette, or a flute, can mean the difference between losing your will to live, and going on.