I believe the best practice is to carry an LED flashlight with multiple light levels as part of your everyday carry that is also good enough to double as a backup headlamp on the brightest setting, and to keep a power supply available that is adequate for at least one ride. I carry 2 mini bungee cords in the kit I carry when riding, which can be used to attach my flashlight to the frame. My current EDC flashlight is a 1xAA light (the perfect size for pocket carry), and I run it on a NiMH battery that I charge periodically.