One of Jack's most significant actions toward the beginning of the novel is his insistence on being in charge of the hunters. He decides to volunteer to maintain the signal fire on the top of the mountain.
Another important action that Jack takes is painting his face. The act of face painting is symbolic for the hunters, as it allows them to liberate themselves and rapidly descend into savagery.
Jack's decision to call his hunters away from the signal fire and to his successful hunt is a major turning point in the novel. The boys not only miss a rare opportunity to be rescued by Jack, they also develop a bloodlust for hunting pigs.
In chapter 8, Jack attempts to usurp power by publicly criticizing Ralph's leadership, and he holds a vote to remove Ralph from power. When Jack receives no votes, he quits Ralph's tribe and establishes his own tribe of savages at the opposite end of the island.
Jack leading the boys in their ritual chant during the storm in chapter 9 is also a significant action: it results in Simon's brutal death on the beach.
Jack's decision to raid Ralph's camp in order to steal Piggy's glasses is also an important action, which leads to a showdown between Ralph and Jack in the next chapter. After Ralph confronts him, Jack not only demands that his hunters tie up Samneric, but he also throws his spear at Ralph after Roger brutally murders Piggy.