The requirements of a "survival flashlight" vary from one person to the next. Is high output required or should you go with long battery life? Common everyday batteries or high performance lithium-ion rechargeables? Hand held or headlamp?

I don't own a "survival" flashlight, but I keep a FourSevens Quark Tactical QT2A-X in my truck's survival kit with lithium primary batteries and NiMH rechargeables. I also keep a single mode 1xAAA (think Arc AAA) w/ lithium primary in my Mission Wallet for pocket carry. (there are a lot more lights than that here from Fenix & FourSevens and headlamps from Princeton Tec & Black Diamond)

Different lights will be better suited to some situations than they are to others. My primary recommendation is to think about how you will use the light and what you will use for fuel. Lithium batteries have great shelf life and excellent operational life. These are great for short term survival such as your typical 72 hour requirement, but for longer than that think quality rechargeable NiMH in a size that works. For me, that means mostly AA with some AAA for the smaller lights and other small devices that require AAA batteries to be small.

Work out all those details and choosing a light becomes a bit easier.