Depending on what your plan of action is in case of an emergency and where you might be at the time and where you plan on going - if you can do so, having a dependable light source is essential. Most commercial "survival kits" found online are just garbage with 50 cent flashlights.
Let's try and drill down here so you don't waste a lot of time and effort in acquiring the wrong tools and ending up in a world of poo.
Keep in mind that every item you acquire for the purpose of being prepared should have more than one use - same with flashlights. That said, if you have more than one type of light and they use more than one type of power source (other than say crank powered lights) you need to reassess. If you live in cold climates and need a reliable light it must be powered by batteries that work in and can be stored in cold temperatures without loss of charge.
Remember batteries work by a controlled chemical reaction...the colder it is the less reaction is going on. Lithium and lithium -ion batteries work down to 40 below and can remain charged up to 10 years ( I have some still charged going on 17 years!) There are some batteries that will not work until they are twisted to start up the reaction (Code Red) and these can store 20 years. But to keep it simple (KISS) having a light that requires little effort to turn on is best - you may be injured and have limited use of your hands.
Large deer jacking spotlights with cords or 6V lantern battery lights are heavy and while provide large amounts of light, are simply too big. Old fashioned 2 cell D lights and bulbs are out as well - too fragile. Miniature lights..you know the answer - with the exception of Innova MicroLights and Princeton Tec key chain lights or a Princeton Tec Blast Light....carry them always.
Rechargeable lights are great tools for cops and fire/ems as they need them every day. Maglite, Streamlite, Laser Products, Pelican are some well made (and expensive) lights. Innova Lights are hard to break and offer economy and performance using lithium batteries and LED's that will last forever. Some lights are waterproof and others weather resistant...make sure you know what you want...and are willing to pay for. Cheap imitations are just that...cheap imitations and when you really need them...they generally fail. Carrying spare bulbs can add weight as they require protective containers to store the bulb and reflector as one unit. LED's are permanent.
Rechargeables usually last about an hour to an hour and a half unless you pay a lot more for heavy units that can last up to 5-6 hours....firemen carry these. Laser products offers plenty of models in small sizes and also lithium models that are pretty much top of the line - I have had the original 6P model since they came on the market in the 80's and it still uses the original bulb. The military and police services use these a lot as well. Drawbacks - battery drain is high and if you are not disciplined in using the light you will have a dead lamp real soon.
You can choose to carry a lot of CR123 photo batteries - and they are cheaper now....and the batteries come in a rechargeable RCR123 version....solar charging can take some time (especially in the northeast) and there is weight again...but may prove useful if you use this in conjunction with a RCR123 powered UV Steripen for water purification....don't rely on multiple battery platforms or you will go crazy trying to keep them all powered.
First Choice.....Innova 5 LED Lithium powered lamp at about $34 average at Brigade Quartermaster or Target stores. They have a lanyard so you can hand in a shelter and will last 20 hours on one set of batteries - plenty for a 3 day bug out. You can get a case of twelve CR12 Batteries for about $20 or less....Carry one in your car(s) and purse and bug out type bag with some spare batteries wrapped in a paper tube or suitable--- protection so you can find the batteries and use the paper to start a fire or write a note. The light is bright enough especially in total darkness but it is not a spotlight. Carry on your belt or in a pocket.
Need a spotlight using halogen lamps...then spring for the Surefire 6P or G2 Nitrolon in Polymer -$36. Get the Yellow colored version so you can find it after you drop it...you will drop it... There are high output bulbs for the Surefire lights that only work for about 20 minutes on a set of batteries - don't get those. Maglite and Streamlite make a stun strobe light that is super bright but good only for police work or home defense. Let's not be dreamers here thinking we will be lighting up the Super Dome.
Gadgets cost money and take up space and are heavy.
Remember you want a light that is unobtrusive, durable and can work for long periods of time.
Always have a key chain light on your key chain or bag...they have 2 light levels and a strobe...imagine that. You will use these all the time once you have them. Good.
If you opt for something different...a headlamp is a good idea. You can power these in a variety of ways...AAA, CR123's, AA, 9V.....you pick.....it is on your head so think about weight. Belt power packs are too cumbersome. 1 Watt LED bulbs are plenty bright. Black Diamond, Princeton Tec , Petzyl, are good brands. Brigade has some good lamps ... http://www.actiongear.com/
In summary: small, durable,LED, Lithium powered, simple on/off with push button. More later.