Here in California (mostly open space, rare clouds, a lot of light pollution from large cities), I prefer to use no flashlight at all as in most cases there is enough scattered light available at night for the natural night vision. After 2 hours in darkness you will be amazed how much you can see without a flashlight and how little with it.

However, when in the field I'm always carrying the Wave multitool and Petzl E+Lite on my belt. E+Lite is the smallest multi-function headlight on the market and also has the red light modes, which will not ruin your night vision too much but allow to see in really deep night shadows. It runs for very long time on a pair of lithium coin cells for me.