There are many examples from the Lord of the Flies that speak of an allegory. Let me name a few of them for you.
First, the story is an allegory of society. When there is structure, rules, and regulations, then there is order. However, with the absence of these things, then there is chaos. In fact, there is a fine line between order and chaos. The breaking of the conch is a symbol within this allegory that all order is now lost.
Second, there is an allegory to the story of Christ. Simon is the Christ figure. His is not only the most religious one, but the one who is "sacrificed" on behalf of the boys.
Third, the book can be seen as an allegory of the human condition. There is savagery in all of us and it does not take much to bring this out.