In Lord of the Flies what dangerous toy do the boys discover and play with near the end?

The boys don't discover or play with any toys in Lord of the Flies. In chapter one: The Sound of the Shell Ralph finds he conch shell and blows it. The conch is never a 'toy' it is a practical tool and a symbol of civilization & democracy. The only other thing which was found was the body of the dead parachutist on the mountain top, hardly something which could be described as a toy. I suppose at a stretch you might refer to the initial rolling of boulders from the top of castle rock as a game but by the end of the book they were not viewed as toys but as weapons.