Previously, I wrote about how the headlamp is a useful piece of non-photographic gear for the outdoor photographer. Of even more importance, in my opinion, are knee pads.
When you shoot at low angles, you often need to get down on your knees in order to see through the viewfinder. If, like me, you have bad knees, this is not exactly a pain-free action. Furthermore, the ground on which you would kneel is often rough (e.g., a rocky beach), or cold, or wet, or otherwise quite uncomfortable for kneeling. Knee pads deal with all of these discomforts. They provide a nice cushion for bad knees, insulation against the cold, and a barrier against moisture. And at about five bucks for a cheap pair, they are probably the cheapest piece of kit you can get for photography.