After the End: The boys were on a plane fleeing the soon-to-be-nuked UK. Partially averted in that, though the home country is apparently in dire straits, the British Navy is still out doing its job as best as possible. May have verged into Cosy Catastrophe if it wasn't for the fact that mention of the war was a very minor framing device with little direct bearing on the story.
Ambition Is Evil: Jack. His desire to be leader is evident from the outset.
Animal Motifs: A sow's head on a pike, slowly decaying, serves as the metaphor for the decay of children's morals, thus making them closer to hoglike greed.
Artistic License - Physics: The divergent lens of Piggy's glasses (required for his short-sightedness) would be useless for lighting a fire. You would need a convergent lens, found in reading glasses.
It's easy to assume Piggy is farsighted until, at the beginning of chapter eleven, it says: "Piggy sat expressionless behind the luminous wall of his myopia." The concave lenses needed to fix myopia are incapable of focusing light to a point, thus incapable of starting a fire. Whether Golding was unaware of that distinction or had myopia and hyperopia confused, the net result is a clear-cut case of Did Not Do the Research.
Butt Monkey: Piggy, oh so much. He is the one person who can unite everyone else...because they all enjoy laughing at him and feel connected by excluding Piggy. Even Ralph.
Deus ex Machina: Ralph is rescued by the Royal Navy at the last minute, effectively out of the blue. This was intentional, as the Naval Officer is important in rounding off the themes of the story, and the sudden abruptness with which he appears (with absolutely no foreshadowing) is crucial to highlighting the rapidity with which the appearance of an authority can change everything.
Dewey Defeats Truman: Lord of the Flies is actually set in the near future (of 1956), after a nuclear war between the USSR and Britain. This is mentioned by some of the boys in the book (along with the existence of nuclear bombs and their use), although usually in passing.
Double Entendre: The scene where the screaming sow is killed with sharpened sticks is written as a gang-rape...
The scene where the kids reinact this, using Robert as a replacement pig, is even worse, what with lines like "Ralph too was fighting to get near, to get a handful of that brown, vulnerable flesh."
The Dragon: Roger becomes this to Jack as his tribe's executioner.
Dying For Symbolism: The makeshift society gradually goes into chaos, and when Simon dies, it represents the death of the innocence of the kids on the island.
Enemy Within: "Maybe there is no monster on the island. Maybe... it's just us..."
Four Temperament Ensemble: Ralph is Sanguine, Piggy is Melancholic, Jack is Choleric, and Simon is Phlegmatic.
Genre Savvy: Ralph describes being on an island "Like a book." Which causes many of the littluns to name out titles such as "Treasure Island" and similar stories.
He Who Fights Monsters: Jack and his choir and eventually almost every boy on the island turn into savage beasts in their obession with killing the beast.
Inferred Holocaust: The navy shows up at the end to rescue the boys. It seems like a happy ending...until you remember that a nuclear war had been going on at the start of the book, which means that Britain (and the rest of the world) is most likely in a sorry state. Not exactly the best thing to come home to after struggling for survival on a remote island.
Irony: Ralph wants to keep the fire lit to attract rescue. Jack wants the fire snuffed out so their fun won't end. Jack manages to draw the attention of the Royal Navy by setting fire to the entire island in an attempt to kill Ralph. It is implied that they wouldn't have noticed the island at all otherwise.
It Gets Easier: Roger escalates from hitting "littluns" with rocks to leading the boys in killing Simon in mass hysteria to outright murdering Piggy.
Lampshade Hanging: The officer who rescues them just as Ralph is about to be killed remarks, "Just like Coral Island, eh?", with said book being one of the cheerier Rousseau Was Right novels.
"Kill the beast! Cut his throat! Spill his blood!"
Meaningful Name: Three of the main characters are named directly after Coral Island characters. The fourth? Simon from Peterkin.
The Messiah: Simon, who understands a lot more than the other boys. The description of his death makes it sound like an atonement sacrifice, which only makes it worse when Senseless Sacrifice it doesn't actually help save anyone.
Nice Job Fixing It, Villain: Jack has the entire island on fire to kill Ralph - the massive amounts of smoke actually summon a Naval ship, which Ralph and Piggy had been awaiting the whole book long.
No Good Deed Goes Unpunished: In order to soften the blow of losing his leadership to him, Jack declares Ralph leader of the hunters. This earnest gesture can largely be seen as the beginning of the end, as it inadvertently sows the seeds of a rival faction with Jack at its head.
Oh Crap: Ralph, upon seeing Sam and Eric fighting each other, realizes how screwed his order is.
One-Scene Wonder: The titular Lord of the Flies only appears at the end of chapter eight.
Only Known by Their Nickname: Piggy, whose nickname started out as an insult. Ralph never bothers to learn his real name.
Only Sane Man: Piggy and Simon. Possibly Ralph as well.
Putting on the Reich: Jack's attitude, rhetoric and eventual reign over the other boys have strong shades of Nazi Germany. His mud mask is a striking design in red, white and black...
Rule of Symbolism: Most of the book. Jack insists on being called "Merridew" and leads a choir. Eventually, after he discovers how to kill, his group degenerates into savagery. Sound similar to the story of anyone we know? Oh, and the spectral corpse on the mountain that terrifies everyone is the Shadow of War, harmless in fact (the pilot is dead), but terrifying to look at. So the choir is like a choir of angels, but what is "Merridew" a reference to? The, ah, 'spearing' of a mother pig.
Satan: "Lord of the Flies" is a literal translation of the Hebrew "Baalzevuv", root of the modern "Beelzebub". *
The ancient Philistines worshiped the lightning god Ba'al, referring to him as "Ba'al Zebūb", or "Lord of Zebūb". "Ba'al Zebūb" sounds very close to "Lord of the Flies" in Hebrew. The ancient Israelites used this fact to mock their enemies.
Shout Out: Golding wrote Lord of the Flies partly to subvert children's adventure literature, in particular The Coral Island by R.M. Ballantyne, which also provided the names of Ralph and Jack. The Naval officer even has the following line:
"I know. Jolly good show. Like the Coral Island."
Single-Minded Twins: Sort of. Sam and Eric are separate people, but separately, they can't do anything. They are treated as one person: Samneric.