Is a writer truly ever doing nothing? Are we ever off duty? I don't think we are. In my experience, wherever I go, whoever I see, whoever I strike up a conversation with, whatever I overhear, whatever I notice is fair game and gets written down or noted in my head, ready for use at another time.
This can be both a blessing and a curse. It's a blessing because I am never short of anything to write about, but it's a curse because it sometimes drives me mad when I can't switch off from it! I know. I can't have it both ways. And, if I'm honest. I'd rather have my head buzzing full of ideas rather than none at all.
The issue then becomes which idea to go with first. To iron out this crease I tend to write down the first three that spring immediately to my mind as if I've remembered them then they obviously have something about them by virtue of the fact that I've remembered them off the top of my head! Then I can expand on these three ideas and see which is a short term project that I can get done fairly quickly - these tend to be letters or fillers, which is a medium term - usually an article with a deadline I can park until later in the week, and which is a longer term project - usually larger articles or a series of articles that I can do the preliminary research for now, but don't have to think about finishing until a month's time, for instance.
So never think that just because you aren't engaging in the physical act of writing that you aren't writing at all - because you are. If you're thinking about it then you're writing about it in your head. The important thing is to get past that stage and actually write, though. Don't keep it all in your head or you might never get it published!
Happy thinking and writing