As a writer, you're never off duty. Sat on the bus for example, you're listening to the conversations around you, looking for story fodder, maybe imagining the scenarios that led to the man on the bus talking about his cuts to his arm - had his house been broken into by a burglar armed with a sword whom he successfully fought off? Maybe he is a self-harmer, with deep psychological issues. Or he's a professional fighter?
And then there's a song they keep playing on the radio, you absent-mindedly start to rewrite the lyrics to make it funnier or different, to amuse yourself.
I had that song by Beyoncé playing over and over in my head earlier: If I were a boy. I couldn't get rid of it, even by thinking of other songs. So the creative writer in me started playing around with the words....
If I were a goat
I'd eat up all of the grass
I'd nibble anything I wanted
Like the roses at the end of the yard.
Silly I know, but it's my creativity in action. Even if nothing comes of it, just messing about like that, your creativity is still stimulated, and should be of use when it comes applying your creative thinking to writing a story, poem or novel later on.