As others have said, carrying an extra Photon is a great idea. The Fenix E01 or E05 are also good ideas, as they use AAA cells. Either weighs 0.7 oz with a Lithium AAA (about 2X the Photon). The E05 is brighter, has a nicer tint (the E01 tends to be blue-ish), and has a nice floody beam, but the cell only lasts about (I think) 3 hrs., whereas the E01 gives a solid 6 hours (with a diminishing light level giving an additional ~12 hours of usable light). The 3 hour figure sounds short, but with normal short-spurt use, that translates into weeks of daily use.
If you want the longest lasting Photon, get the yellow one. It only uses one battery (CR2032), and the current draw is very low with yellow LEDs (as well as red and orange). The only problem is yellow is kind of ugly, muting all colors into grayish-yellow haze, making it awful for determining which wire to cut to defuse bombs :-)
Personally, I wear a NVG green photon with a single CR2032 (instead of the stock 2X CR2016 cells) just about 24/7. The single cell is less bright, but lasts much longer. The NVG green, when adjusted to the barest amount of light necessary, makes everything look a very high-contrast black-and-white. I believe this is because the human eye is most sensitive to this green wavelength, so it needs much less of it to see (shapes), thus it's use in night-vision goggles. That said, nothing beats a micro-lumen pure white light as you'll find on a Zebralight headlamp or flashlight for rummaging in the tent or even the campsite.