Those essentials should definitely include a quality headlamp, too, in case a quest for an elusive geocache catches you out after dark.
Otherwise, prep for geocaching as you would for a hike (or an urban stroll) from the parking area to the geocache location. For a hike, that means considering the Ten Essentials as a starting point. Those essentials should definitely include a quality headlamp, too, in case a quest for an elusive geocache catches you out after dark.