It will hold many 2-C size flashlights as well, though that gets more than a little bit unwieldy. The best headlamps I've found are by Petzl. A wide integral clip which worked on hat visors or pockets, side clips, optional Velcro attachment and elastic headband make it a versatile performer, despite the somewhat lesser beam quality, the same as the MityLite and Magnum, respectively. Not perfect at any one thing, but very adaptable. The VersaBrite II, with it's larger head and better reflector, is the best choice of the two and could easily function as a kit's sole flashlight.
Batteries Use only alkaline or lithium batteries for survival kits.
If the batteries you buy are not dated, always mark them with an expiration date. Better, in my opinion, to replace batteries prematurely than to risk failure in the field. The cost, even for lithium batteries, isn't so high as to be worth the potential for ending up with duds. I rotate my batteries conservatively and then use the ones taken from the kits for everyday duty. I have always used Duracell brand alkaline batteries and I have had good luck with them.