Now and then we come home from the fabric store with a few cardboard tubes that have been emptied of their fabric. The store just has them in a bin by the counter and we just help ourselves, we never ask and nobody objects, so I guess it's OK.
They get used for various things, and sometimes I curse them as they fall loudly on our hard floors, or I step and trip on them (ouch), but they get used by the boys for hours of entertainment (rules: no swinging, hitting and keep them down low). Eventually the cardboard disintegrates (or I get thoroughly sick of them) and we toss them away and get new ones another time.
The best is rolling matchbox cars down inside them. The small boy likes the action of the popping the car into the tube, the big boy likes how the cars shoot across the floor as they exit their long and sloping tunnel.
Yesterday afternoon it was cold and it was just the two of us inside with the heater on. He rolled with intent and concentration, I played chief toy car retriever. I'll let the pictures do the talking.