It would make sense for somebody traversing dark caves and ruins to carry something as simple as a flashlight (and perhaps we're supposed to believe the character has one, because all these places are somehow bright enough to see in). One of the many real-life attachments added to guns are flashlights. In underrail, a tin can gunner has to choose between nvg's and metal helmets (which give a per penalty in addition to not having nvg), but with a flashlight on the gun they could still avoid the darkness penalty (and maybe give enemies some kind of penalty for having a light shined in their eyes). So, either as a weapon enhancement or perhaps as a utility (or you could just let helmets have NV visors or something), and they could require batteries like other powered items. Also, there's those strobe flashlights for guns that are supposed to disorient your targets; another potential thing to add.
