what weapon does jack posses?
Jack possessed more than one weapon, in the sense that he had the physical weapon of a knife, probably a pocket knife, left in his possession when the "pod" crash-landed on the island. At first, the knife is a relic of the boyhood he has left behind that he can't use for something as awful as stabbing the first pig he encounters. As time goes by and as savage instincts come to power, Jack discovers he can use the knife effectively for the purpose of killing.
Jack also possessed weapons that were not actual objects. He was the tallest boy on the island and was already recognized as a leader by the members of the choir. He was not afraid to speak out and to express his opinions forcefully, and he preferred action to discussion. These characteristics all served him well in the struggle to reach and preserve a position of leadership among the others on the island.