I scribble notes in a calendar. What I saw, what I harvested, things that stand out.
Like you, I wish I had written down more extensive notes in years past. I went about 10 years without recording anything.
My grandfather used to keep a calendar and a notepad on the table. He'd sit and scribble in them every morning while having coffee. He'd record who he talked to, how much rain, critters he'd seen, fish he'd caught, all that stuff. After he passed, all that stuff kind of disappeared, and nobody seemed to know what I was talking about when I asked. It's one of the things I remember about him, sitting and talking over coffee, bacon and eggs while recording his thoughts.