While I haven't used one myself, for something like a 72 hour bag a Petzl e+LITE seems to fit the bill pretty much perfectly. This is a headlamp designed specifically for this purpose (i.e., being tucked away for emergency purposes only).
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Victory awaits him who has everything in order — luck, people call it. Defeat is certain for him who has neglected to take the necessary precautions in time; this is called bad luck. Roald Amundsen