There are many literary points you can make. Here are the most dominant ones.
First, there is the symbol of the conch shell. This represents civilization and order. When the boys blow the shell, they know to meet. Moreover, it creates order, as the one who holds the shell has the right to speak. So, when the shell is broken, it foreshadows a loss of order and civilization. Chaos and savagery now reign.
“The conch exploded into a thousand white fragments and ceased to exist.”
Here is a quote that shows the growth of savagery:
“Which is better--to have laws and agree, or to hunt and kill?”
Second, Piggy and his glasses are another powerful symbol. This symbol represents rationality and science. If you recall, the boys use the glasses to start their signal fire. So, when the glasses are broken, it shows that reason will be trumped by base desire and raw passions. Here is a quote:
“Are we savages or what?”
Third, the idea of the beast represents fear and the base desires of all humans. As the boys deteriorate further, the beast becomes stronger. Toward the end, it is deified.