I've kept one since 1992 that logs all steelhead, salmon, and sturgeon trips. As it fills up, it is becoming increasingly valuable as I can now mentally map run timings and stretches of river that produce consistently at certain times of the year.....you do notice trends.

I'm not one given to lengthy, wordy entries but I do always note fish caught, how many, where, water quality (vis and height) and what they were caught on. In the case of saltwater salmon and sturgeon, I also include what part of the tide the action occurred.

I should also note I only record trips where I had action or got some vital info. from a reliable source.