Looking at that Parametrik list sorted by weight, other than the Flare and e+LITE already here, the lowest weight non-discontinued, non-"tactical" model seems to be the Princeton Tec Remix Pro which uses a CR123A and weighs 66g and costs $45 and is plastic. It does seem like a nice light, and I don't mind plastic. But it seems like everyone wants high-lumen lights now, which use more battery power, which means bigger batteries and more metal mass to handle the heat. It is possible to select just the metal ones like this:

link

A lot more possibilities open if you can use 2aaa or 3aaa. The Black Diamond Wiz (2aaa, 56g, intended for kids) looks interesting because of features like a 2 hour auto-off to prevent the batteries from draining if the light is left on.

Doug, would you be buying 100s of lights at a time for those kits? Maybe you could convince Fenix to do another run of the discontinued HL05 or HL10 lights by offering a large enough order.

Addition: thought I'd mention I just got a couple of Litezall 3aaa headlamps at $3.50 each: https://sidedeal.com/deals/2-pack-litezall-mini-headlamps-3

They are lightweight (24g for the light, 6g for the strap, 63g total with 3 alkaline AAAs or maybe 50g with lithiums) and have an electronic switch which is sealed. They stow pretty small since the headband is just a piece of elastic with an adjustment clip, no stiffener needed. They have a hinged backplate to put in the batteries, so the seam around it is the most likely place for water to get in. I think they would withstand a good splashing as-is but they aren't truly waterproof. I haven't yet measured the operating current (to estimate runtime) or the parasitic current (which might matter for long term storage).

If there is parasitic current, that could be handled by putting a little slip of paper to insulate one of the battery contacts during storage, which would also protect from accidental turn-on. If there is no parasitic current and you want to leave the batteries in the light, you could probably seal the battery compartment with tape or clear nail polish around the seam. I like these lights and plan to stow one in my glove compartment.

Based on the 120 lumen claimed brightness on high, pending measurements, I'm going to guess power consumption at 1 watt on high or 0.5W on low (PWM), giving runtime of 6h high or 12h low with lithiums. They should also have a long reserve of lower brightness.