Bear and J-jo really love the book The Button Box.
We did some fun button activities to follow the book, like threading buttons, sorting buttons, carrying buttons around everywhere (for Mommy to find strewed all over the house). We also glued buttons to make collages.
But a really fun thing we did with the buttons is make sun prints on special sun printing paper I bought with a coupon at JoAnns a long time ago.
The sun turns the paper all white, then you “develop” the print in water to prevent the paper from being further exposed.
You may be able to do this with cheap construction paper, but you would probably have to keep the collage in the sun all day.