What items can be used to represent Jack? (I need items that are not obvious like a knife but more interpretive like a broken pair of glasses Thanks.)
The first suggestion might be something representative of Jack as a bully. Iron knuckles or some other type of weapon/implement that could be used to intimidate others and force them into submission would certainly reflect Jack's relationship with Ralph, Piggy and some of the other older boys.
Another possibility might be a compass. Jack obviously did have some valid leadership abilities. He was recognized by the others as being able to give them directions that they were willing to follow; he led them in searching for the beast and for the pigs that allowed them to have meat to eat.
Blinders, like those used on horses, could be interpreted as indicating that Jack was not open to differing opinions. He knew what he thought was important, developed his ideas about how things should be done, and wasn't willing to give much weight to any suggestions of other approaches or concerns.