Jack trying to convince the other boys that he is more fit to be chief than Ralph shows Jack's disregard for authority and civilization.
Ralph letting the fire go out in Chapter 10 symbolizes how Ralph has finally lost hope of ever getting rescued
Roger killing Piggy with the boulder and none of the boys in the tribe showed remorse. This shows how savage the boys have become since they came on the island.
The conch symbolizes civilization, order, and authority. It would be used by Ralph to call the boys to an assembly. Whoever held the conch would be allowed to speak while others would remain silent. When the conch broke into pieces when Piggy died, it signified that there was no longer such a thing as order on the island.
The fire represent hope, comfort, and destruction. Ralph wanted the fire to give off smoke for any ships to see if they pass by. This symbolizes his hope of getting rescued. In Chapter 10, Ralph admits that the fire had a double meaning. It also served as "a hearth now and a comfort until they slept". The fire symbolized destruction when Jack and his tribe used the fire against Ralph to try and kill him.
The Beast symbolizes the boys' fear of the unknown and their inner evil. The hunt for the beast and paranoia that it could come at any moment push the boys into killing pigs and Simon who was disguised as the Beast.