Tiny ultra-light, single-bulb LED lights might look like a toy for a keychain, but they’re useful for far more than that. Get a few of them, they’re cheap!
They cast enough light to easily follow a trail in pitch dark, or find that rappel anchor heading down from a longer-than-planned alpine day.
Consider putting a shoestring on it, or it’s going to get hopelessly lost. A shoestring lets you to keep it comfortably around your neck, even when you’re sleeping. You could also girth hitch it to a loop inside your tent. Use it as an in-tent light rather than blasting your tentmate with your face-melter 300 lumen climbing headlamp.
Get one that has a switch to turn it on without holding constant thumb pressure on it - not all lights have this feature.
Make a “lantern” in your tent - turn on a microlight, put it on top of a water bottle, and then either tape it or put a sock over it to hold it in place. The light will diffuse through the water, casting a soft romantic glow over you and your smelly climbing partner.
Keep one in your first aid or survival kit for hiking - no need to carry a heavy flashlight as a backup on hikes when an LED light will probably light your way out in an emergency just fine.
Tape one inside your helmet. Does your chalk bag have a zipper? Put one in there. Car glove box too. Buy a bunch, keep them in various places.
With a couple of these and a climbing headlamp, you should be set for most anything.
Here's an Amazon link to get five of them at a time. If you have a few extras, give them to your pals.