Have you ever considered keeping an "interest log" and just writing down notes of things that interest you? I have been keeping my little notebook of ideas for a while and I have a note app on my phone that I use quite a bit; especially when I can't get to my notebook right away. I decided to put a notepad beside my bed for when I get ideas as I am going to sleep (or if I wake up with one in the middle of the night). I figure it will also help me when my mind starts wandering with things I need to do the next day, I can just write it down on the notepad and then I'll see it in the morning.
How do you keep track of your ideas and interests?