Weaving placemats or coasters with cardboard and yarn or embroidery floss. Great idea for small dollhouse rugs!
DIY Rug from yarn and cardboard tutorials I'm gonna try this with all my yarn from my frustrating failed attempts at knitting scarves n whatnot.
DIY pom pom rug using a non-slip rug mat! Probably cheaper than an actual rope door mat
Turn a cardboard box into a fun storage bin or fill it with party favors at a party, etc. (I use boxes for everything; this idea will really come in handy around my house