I don't generally plan on doing much riding after dark while touring, but I do carry a bike light and a small headlamp (the latter is mainly for camp use but also as an additional 'be seen' light). I try to standardize on NiMH AA and AAA cells for the lights, GPS, camera, etc. so that I can swap cells between items when needed and only need to carry a single lightweight charger. Many campgrounds have outlets available and other times I've asked if I could plug the charger in somewhere in a restaurant while eating there.