“Be careful! Don’t hit the girl!”
“Over the top, boys. Charge!”
GAME OVER, MAN!
Yeah, TOO quiet…
Where? Behind that rabbit?
May The Force be with you. (Depends on how strong The Force is with that one.)
“What? Do you want to live forever?”
He’s on your tail! I’ve got him …
<ear-shattering scream>
That’s a word, right? 
One from real life:
John Sedgwick: “They couldn’t hit an elephant at this distance.”
Geronimo!
Look out below!
That was obvious. The one who wasn’t a regular or a Special Guest Star.
Replacements: The Redshirts of COMBAT!
“It’s a dud.”
Similarly
“Stop worrying, none of this stuff works anymore.”
“What could possibly go wrong?”
In old war films: “Here’s a photo of my girl back home.”
“I got a real bad feeling about this.”
“You haven’t got the guts to pull that trigger.”
::knocks on door of creepy old house and enters:: “Hello? Anybody home?”
“This wallpaper is killing me, either it goes or I go.”
Wanting to “write that letter home” would get you killed faster than just about anything else!
Captain? There’s something over here, sir!
That’s funny. Don’t think I’ve ever seen anything like this before…
Kowznofski! Get down!!!
“I don’t believe in Ghosts/Demons/Spirits/Supernatural Beings”
“I’ll check the basement.”
“I’ll take point, sir.”
“Don’t worry, I got this.”
Trope namer!: Sedgwick Speech - TV Tropes