Create 1 - 4 post cards incorporating pieces of calendars that show numbers. days/months/words, but not the picture parts. Aren't you glad I listed this swap before you threw them all away?
Any background is allowed. The calendar bits need to be a prominent, obvious part of your whole design but you may use other media as well.
Think squares. triangles, strips, circles, etc. Torn, cut, punched-out, etc. You may include ink, paint, rubber stamping, stenciling, etc. Just be sure the pieces of calendar are recognizable, not completely painted over or obscured by other images.
The backgrounds for my samples were from a large APPLE poster. I collaged pieces from three or four different calendars, some of them colored with rubber stamp ink.