Originally posted by GunsForBucks:

cargo floats in crates
stuff on your person will be in floating gravestone

Ship parts will be on the bottom

To add to this a bit. If you have open inventory slots, enough carrying weight available, auto gather turned on, and you stand on the ship's mast when the serpent breaks your ship the ship parts will go into your inventory. When the serpent kills you the parts will be in your floating corpse's inventory.