What is in the container that damages the boat in the film 'All Is Lost'?

In the film "All Is Lost," the container that damages the boat contains a large quantity of metal debris, specifically a shipping container that has fallen off a vessel. This debris punctures the sailboat's hull, leading to a significant leak and ultimately putting the protagonist's survival at risk. The incident serves as the catalyst for the sailor's struggle against the elements and his fight for survival at sea.