Continuity mistake: Bernie gets shot underwater with the spear and can't let go of the chest. But when they take the vest off Larry to float Bernie up to the surface, Bernie takes his hand off of the handle to get the vest on.
Plot hole: In Weekend at Bernie's one, Larry takes Bernie's watch and never puts it back on the body. In Weekend at Bernie's II, he gets the watch at the morgue after it's been taken off the body, and signs for it. How did the watch get back on the body?