Some people seem to think about their current project whenever they are doing mundane, routine tasks. That has never happened to me unless I make a conscious effort. I wonder why that is, but I have no answer.
I guess there must be other writers out there like me, and I wonder if they try to remember to think about their stories while doing other things. It does save time when you finally get to sit down and write.
I heard that another good thing to do is to go over the story in your head just before sleep. I rarely remember to do that, either. I don't know WHAT I think about before sleep. Nothing much, I guess.