To add to what the other editors have said, you might mention that Jack is hedonistic.  He lives in the here and now.  His mantra is "We'll have fun on this island."  He has no use for long-term goals of rescue or shelter.  Instead he enjoys the thrill of the hunt and resents anyone who stands in his way of his savage-like pursuits.  He continues to roll rocks when Ralph has clearly abandoned such pastimes.  When he is not not elected chief in the second election, Jack declares that he doesn't want to play anymore.  Jack cannot get past the fact that the survival on the island is more than fun and games.  He operates solely on the principle of pleasure/pain.  What brings pleasure to him is good; what brings pain to him is bad.