Often in my planner I write notes to my future self.
Sometimes these notes are straightforward information. For example: my kids' school allows us to check out books from the library over the summer, after paying a $150 deposit. On my weekly notes page the week school starts, I have written a reminder to myself to take the deposit form to the school and collect my refund. I even noted where I filed the deposit form, since I'm apt to forget.
In the past I've written other notes to my future self in the form of questions. A few years ago we went to see a town where we were considering moving. In my planner on the first day we were scheduled to be in the town I wrote, "What are my first impressions?" On the last day of our visit, I wrote, "Do I think I would like to live here? Why or why not?" The answer was, definitely not. Question answered.
Do you ever write notes to your future self in your planner?