Since your group has three members, you could choose a person to play each of the three major characters: Ralph, Piggy, and Jack. Each could create statements or act out in gestures to narration their beliefs about civilization. Ralph's focus would be on the importance of rules and the conch, whereas Piggy would be hopeful that having strong leadership would protect him from mean-spirited bullying. Jack, on the other hand, would challenge both characters and could maybe appear wearing his painted mask and brandishing a spear. Over-exaggeration of each boys' characteristics and beliefs would make your skit more memorable and effective.
Rules and order in the book are completely demolished and basically broken from the core. The boys begin to fall apart at the seems and they lose touch with everything that once linked them to society. In a sense, they lose what defines what we consider to be human-like qualities; they become animals in the wilderness. A skit portrying this would capture the idea brilliantly.