An old house thats about to be demolished. Once my friend was about to expand a room and needed to knock a wall down, I offered to help, and we smashed it down with sledgehammers. The wall wasn't load bearing, but we built a support for the ceiling for safety.
A cheap $50 car from the wreckers, try to compact it into a small cube (I've never done this, but I think it would be fun), make sure the petrol tank is empty, leave the cap of for a week to make sure it all evaporates.
Breaking things when sledgehammer training makes it satisfying.
A tire is most practical, and it gives a recoil.