Originally Posted by DJ Niner
A small notepad and writing implement(s). Useful for recording general observations, thoughts, things to do later, maps/lay-of-land/directions, people movements, resources seen while moving through an area, storage caches for future use, areas to avoid, etc. Many, many uses.
^^^ This! Didn't even think of that, but it makes perfect sense. It'd take me all of an hour to wish I'd packed a pen & pad.