I have tubes large small, PVC pipes. they connect them and make awesome creations!
and Pool noodles cut them in half and we make ramps out of them! use bouncy balls to go down the hole! they just love this. (they use the shelf to lean the noodles ramp so they can watch and see who's ball goes down the fastest!)
our classmates faces on jinga blocks...the kids like to play schoolhouse and use their classmates.
oatmeal boxes or Pringles cut out the bottom and they build with them or push cars through it. (tunnels)