A good number of these strongmen workout with unusual equipment. During my heavier-training days, I met a fella in Virginia who had a replica Husafell Stone in his yard. He also had a few round “stones” all weighing upward of 250#, enormous sandbags and a THICK bar on which to load weights.
To this day, I still work out with hand-grippers that require close to 200# of pressure to close.