Caving

Backup Light Source

You of course can never have too many backup light sources in an environment such as this, and glow sticks fill that role very well. While not a substitute for a good light, they can help provided needed illumination when primary lighting methods fail. Additionally should you find yourself stranded for an extended period of time, glow sticks provide needed light long after regular batteries would run out (each stick will glow brightly for 8-12 hours).

Cave Marking
Great for marking entrances or routes taken, glow sticks can be activated and left behind as emergency markers, either for possible rescuers to follow or just to give you a bit of added piece of mind on your return trip. Glow sticks glow brightly for 8-12 hours, and can continue to emit light for up to 24+ hours, so they should last plenty long enough for that added safety margin.