Among other things, I think of annoying extensions/alterations of Murakami's title (which itself is an adaptation of of a Raymond Chandler title).
What I was thinking, partly, was that I could nearly write a book out of the different thoughts that fill one run--to write them all would take at least as long as the hour or two that I was out running....but probably longer, because turning ideas into structured sentences isn't instantaneous. That assumes that I could even remember all the things that I thought about.
I spent a lot of today's run thinking about how thinking aversive thoughts can make things worse. By thinking about how difficult the thing is, the negative anticipation builds up. And this makes dealing with the thing worse. And how you don't want to remind people too strongly of the unpleasant aspects of things that they have to do.
Also considered were: the question of how soon to start exercise after an injury; what my friend was up to at the moment I passed her house; what route I was going to run; how the same group of people managed to get on the same public volleyball courts every week (you'd think sometimes some else would get there first)...there are too many people passed to wonder at every person's story.
I thought about writing, of course. I thought about how understanding other people's stories is the foundation for writing good fiction. I didn't think this then (or at least not as I remember): understanding other people's stories is the foundation of good communication, generally.
Part of what I thought about while running today was how one of the important tasks for the writer is to filter through all the possible ideas that could be talked about, and to stay focused on topic.