Punching bags come in two forms: a hanging heavy bag and a free-standing bag on a weighted base. Hanging bags are dense and awkward, while free-standing bases are often filled with water or sand that should be drained first.
Pro tip: Drain a water base before moving, since a full base can weigh well over 100 pounds and slosh.
Watch out: A filled heavy bag is dense dead weight, so never let it swing free or drop when unhooking it.