A camping lantern, nicessity for home use or car camping or backpacking alike, which is so small and light it fits right on your keychain via a carabiner. Weighing under an ounce and measuring one by two inches, the LED Mini is a perfect back-up light. Throw this in your pocket and forget all about it until the sun dips below the craggy peaks and darkness engulfs you. Then turn it on and light up your tent; though it's small, it outputs 3.5 lumens and is supposedly capable of lighting up an entire tent. Luckily, since it'll be most at home in the backcountry, it will likely just have to provide enough juice for a slimmed-down, ultralight solo or two-man.
If you find yourself in a sticky situation where mere light simply won't bail you out, the LED Mini also includes a strobe setting for catching the attention of other campers. It can run continuously for 25 hours (or 50 on strobe) with the two included 3 volt CR2032 batteries. It may not provide a spotlight for your acoustic guitar solo, but for $6.99 it'll certainly be a valuable addition to your gear closet.