Well, I've done 3 so far, so that's a start.
First, a little chipmunk in a pot plant, while waiting in line to vote.
The next was a little fairy notebook, near the return chute at the library.
And lastly, a tiny bottle of bubbles in the womens change room after the kids' swimming lessons.
The hard part of this challenge won't be hiding treasures, it will be finding 4o more tiny little things (I can bear parting with) to hide!