Thinking through a SHTF scenario where you bug in to a bunker of some sort, you will immediately run into a problem.  Presumably you wish to remain hidden, so you will be below ground for long periods of time.  The sun, as it turns out, doesn’t work underground, so we need a way to light our high speed bunker without electricity.  Here are a couple of ideas:

Solar powered lamps:  These can be great for providing a few hours of light at a time.  Some claim to work as long as ten hours off of a solar charge, and as many as twenty hours off of a 12v plugin.  There are a few problems with this method, however.  First, you need to be able to go outside to place the lamp in the sunlight.  Assuming you can manage that, you need to have multiple lamps so you can use one while the others are charging.

Candles:  This is the way that dark spaces have been lit throughout antiquity.  It’s necessary to stock up on candles if you’re going to use this method, or to learn how to make candles with the ancient, no-electricity-required techniques.  Hmmm…I smell another post coming on.

Mechanically powered flashlights: These are pretty cool.  You just spin the crank and out comes the light.  Granted, it might get a little annoying to turn the crank every few minutes for the rest of your life, but it will work in a pinch and it beats the hell out of sitting in a dark underground bunker for hours on end.