Car Chase: Garbage truck vs. M60-equipped Fast Attack Vehicle. Truck = 2, FAV = 0.
Cell Phones Are Useless: Kevin draws attention to the fact that there's no cellphone reception in Hell as it's too isolated early on. When they return to town to discover that it's largely abandoned, they all check their cell phones in unison, only to discover that they still cannot get reception (presumably as the invading army knocked out the towers). This explains away why no one tried to contact them via phone to warn them, and why they don't use their phones to stay in contact later when they have to split up. The book on which it is based was written before cell phones became so ubiquitous among teenagers.
Concealment Equals Cover: The two girls driving the garbage truck are partially protected by the front scoop (though not the windshield) and heavy steel rubbish container, but there are several moments when they're being shot at from the sides by auto-rifles and medium machine guns. Averted on the occasion when one of them drops a roller door only for several bullets to punch through (she's already ducked out of the way).
Contemplate Our Navels: Ellie and Corrie sit in their old playhouse and muse about how they've lost their innocence and nothing will ever be the same.
Death from Above: Foreshadowed when Lee insists they park the Land Rover under cover rather than leaving it out in the open.
Distracted by the Sexy: Homer gets tackled while he's staring at Fi taking off her shirt to reveal her bikini.
Dr. Jerk: The dentist who treats Lee's bullet wound.
Halfway Plot Switch: There's no lie involved that it's a movie about an invasion of Australia, but the "Teens going camping" part goes on long enough you start to forget what the movie's eventually about.
Hard To Light Fire: The two girls who drive the tanker-truck and prepare the petrol-soaked rope to blow up the bridge both thought the other girl brought the lighter.
Just Plane Wrong: A minor case of it compared to the egregious examples in the books. The enemy fighters look like the fuselage of an F-16 with the wings of a Mirage III-O grafted to it.
They may have been Chinese J-10s, which have features from both craft (Delta wings, chin intake, single engine). The J-10 would fit with the distinctly modern PLA design of the enemy uniforms.
The aircraft actually resembles the Chinese/Pakistani JF-17 Thunder.
Furthermore, the enemy helicopter is a Robinson R44, arguably the least threatening civilian helicopter out there.
It's not just the planes, either: when a enemy fighter launches a missile, it's fuselage is red. Training missiles are red, but a real one would still be gray steel.
Ellie: Ladies and gentlemen... Homer belches. Ellie: ...and Homer...
Lock and Load Montage: The original low-key ending was replaced by the group taking captured weapons out of a crate, strapping them on and standing against the skyline in defiant poses.
Made of Explodium: Amazingly enough, even worse in the movie than the books. The bridge itself explodes after the tanker truck has.
Moral Dissonance: Ellie rips Chris a new one for falling asleep on watch, which risked all of their lives, and tells him to shape up and be more responsible. Later, Ellie and Fi accidentally turn off the radio, talk about boys instead of keeping watch, and both forgot to bring the lighter to set off the petrol-tanker bomb. This nearly gets them both killed, forces Robyn to break her pacifist vow, and gets Corrie shot.
Spray And Pray: Averted when Homer (who's used to firearms) fires just a couple of aimed shots at the helicopter from their captured AK47. Later when the inexperienced Robyn fires she empties the magazine.
Stillborn Franchise: Although the highest-grossing domestic movie of its year in Australia, it still didn't make its A$27 million budget back - and it completely bombed internationally, so adaptations of the other six books in the series are pretty much out of the question.