A work journal.

I know this one seems a bit obvious, but in the workforce, I rarely see people with them.

Work journals are not very exciting. But just writing things down really makes a difference somehow. Those boring meetings become slightly less boring when you take notes. That thing from six weeks ago doesn't slip by you as readily. That person's name on that one call isn't a mystery. Your year end report is chock full of stuff, not just a few .ppt bullet points of a few highlights.

It's pretty straightforward, and just takes about two weeks of practice to get into the habit. For the effort, it really does multiply.