For me, it can be absolutely anything, but then I am a bit of a Dilly Daydream ;).
I've done this ever since I was a child, and not always when I was bored - hands up who has ever had the moment when someone looks at you expectantly and you know they said something, or asked you a question, but you have no clue what they just said, because you were off somewhere casting magic spells, or defeating evil wizards? :).
Inspiration: sparks for my imagination can come from many different places.
A view sometimes makes me want to write as well. I have been lucky enough
So, when I do daydream, or, as I prefer to call it, invest in my writing future, ;P, it comes to me like a film strip. I suppose since I grew up with TV and film, this is how my imagination works, which is great for visual descriptions, and okay for emotional response as well, but one sense I have to remember to engage in writing is the sense of smell. Words, unlike TV, can encompass all the senses, and I think that is why any writer has to go out and experience bits of the world. I don't mean they have to go and stand in a milk factory so they can set a scene in one, but they can use the experience of having mistakenly opened a bottle of off milk to remember that rancid smell of the not-so-fresh dairy produce. Without those little moments of memory, writing would be flat and grey and it is everything we have experienced that feeds our imaginations.
They say, write what you know, which, taken literally would also be very boring, since I don't think people want to know all about writing project plans and timetables for students, which is my current job, but knowing can be adapted and used to spark much more imaginative things. I may not be writing about a project manager any time soon in my stories, but I write about leaders and organisers all the time, and one of the skills I've had to learn as a PM is persuasion, something a writer has to also use both in beguiling their readers and in any scene involving negotiation. So, even the mundane can be the spring board for inspiration. :)
Do you have anything that particularly inspires you?
P.S. Check out other folk doing the A to Z April Challenge.
And if you want to see my other posts:
Sophie's Thoughts & Fumbles A to Z Challenge Posts