16. The Warriors - Come Out to Play!
In this scene, The Warriors' script called for Luther (David Patrick Kelly) - leader of the vicious New York gang the Rogues - to drive up and provoke rival gang The Warriors to a fight in the streets by clinking bottles together.
Kelly spontaneously added the now famous line "Warriors, come out to play!”
15. The Godfather - Leave the Gun, Take the Canoli
Returning to The Godfather, Corleone family capo Peter Clemenza (Richard Castellano) orders his henchman Rocco Lampone (Tom Rosqui) to carry out a hit on Paulie Gatto (John Martino) for his betrayal of Don Vito Corleone (Marlon Brando).
Castellano's original line was "Leave the gun" but drawing from an earlier scene where Clemenza's wife reminds him to bring home some cannoli, he improvised the now famous line "Take the cannoli."
14. Dr. Strangelove - I Can Walk!
Nuclear scientist Dr. Merkwürdigliebe or Dr. Strangelove (Peter Sellers) was confined to a wheelchair for the entire film - but Sellers decided to spontaneously stand at the very end of the film, take a couple of steps and proclaim, "Mein Führer! I can walk!"
In a process known as "retroscripting", Kubrick changed much of the script he co-wrote with Terry Southern to incorporate much of Sellers' improvised dialog, including this now famously unscripted scene from the end of his black satirical comedy.
13. Saving Private Ryan - Wartime Bonding
During a brief break from fighting, Captain Miller (Tom Hanks) sits with Private Ryan (Matt Damon) swapping stories about what it was like back home for them both. The story Damon tells about his brothers and the barn was made up entirely by him during filming.
None of the story was part of the original Saving Private Ryan script.
12. Jaws - You're Gonna Need a Bigger Boat
While chumming the waters in an attempt to lure the deadly great white shark within range, Jaws' heroic Police Chief Brody (Roy Scheider) gets his first look at exactly how massive the killer shark truly is.
Stunned, startled and filled with fear he stands up and utters the now famous line to Orca Captain Quint (Robert Shaw) completely off-script, "You're going to need a bigger boat.”
Turns out, he was right.
11. The Empire Strikes Back - I Love You. I Know.
As smuggler-turned-hero Han Solo (Harrison Ford) is about to be encased in carbonite during The Empire Strikes Back, Princess Leia (Carrie Fisher) reveals her love for him. The script called for Leia to say "I love you" to which Solo was supposed to respond with "I love you too".
Ford decided that Solo wouldn't say something like that and instead, changed the line to simply "I know."
10. Reservoir Dogs - Stuck in the Middle With You
The script for Tarantino's violent, freshman project Reservoir Dogs called for jewel thief Mr. Blonde (Michael Madsen) to torture Officer Nash (Kirk Baltz) by cutting off his ear with a straight razor - however, Tarantino didn't give Madsen any specific direction what to do once the gruesome deed had been done.
All of Madsen's lines and actions with the ear were improvised by him.
9. Casablanca - Here's Looking at You, Kid
The scene of Rick Blaine (Humphrey Bogart) putting Ilsa Lund (Ingrid Bergman) and Victor Laszlo (Paul Henreid) on a plane bound for America with the help of Captain Louis Renault (Claude Rains) is chock full of memorable lines but the line listed as 5th in AFI's 100 Years...100 Movie Quotes wasn't even part of the original Casablanca script.
According to reports, Bogart said the phrase "Here's looking at you kid" multiple times to Bergman while teaching her to play poker between takes.