A lot of guys listed 2 headlights. I've never had one fail and fresh batteries will last me weeks.
Have any had to use the backup head light?
If I'm hiking/backpacking I rarely carry two lamps (spare batteries yes), BUT when I know for certain that a good deal of my time is going to be spent on the trail in the dark (almost all of day hunts include a significant time hiking in the dark, adventure races sometimes the entire night). I had a headlamp give out on me on a trail race that went into the night, fortunately there was another runner close by and he lent me his spare lamp- I figure two ounce insurance.
