BOY WITH THE MULBERRY BIRTHMARK. This boy is significant primarily because only Piggy seemed to be concerned that he is missing. The littluns quickly became the least respected of the boys (because of their youth)--the lowest class of the island's social spectrum. They never learned his name, so his loss seemed insignificant, especially to Jack and his hunters.
THE PASSING SHIP. This missed opportunity could have gotten the boys rescued much earlier, with no loss of life or the gruesome behavior that followed. By allowing the fire to go out, the boys gave up an earlier possible departure.
THE FERAL PIGS. The pigs served at least two purposes: They served to spur Jack's blood lust for hunting, leading to further barbaric behavior; and the pigs served as a prime source of food.
The naval officer's appearance at the end of the novel to save Ralph seems to be a contrived ending. Ralph's death is certain. He is being smoked out of the woods into the waiting spears of the boys on the beach. The fact that the naval officer appears at just this time seems too much of a coincidence.
Yet, it is important thematically to the story. The fact that the rescuing adult is a military man is symbolic of the war that the entire world is engaged in. The island, in this way, is only a microcosm of the world itself. The war on the island is not caused because of some isolated situation of boys being stranded on an island; it is caused by the same reasons that cause all wars: power struggles, insolvable differences, acts of aggression, fear, lack of respect or understanding of those who are different.
As the naval looks out at the distance, his eyes fall on his cruiser. His cruiser is a destroyer. There is no real rescue for the boys. They are only leaving one war for a bigger one.