Arnold Schwarzenegger and Sylvester Stallone are regarded as the best in their field; two musclebound action heroes and leading men who seem to be stuck in a friendly rivalry with each other; it's a mystery to everyone why they don't just work together. That's just their characters in the movie of course. In the real world that was only true in the eighties.
In the sequel Gunnar shows that he is a chemistry engineer. Dolph Lundgren actually is one.
Booker's nickname is Lone Wolf, a play on his film Lone Wolf McQuade. His name itself is a reference to Good Guys Wear Black. He also mentions he was once bitten by a king cobra, and after 5 painful days, the cobra died, a reference to one of the many Chuck Norris Facts.
Jet Li gets to do his specialty One-Man Army routine in the sequel armed initially with his fists, then with two frying pans; while Jean-Claude Van Damme gets to do his specialty jumping roundhouse kicks twice against Stallone.
When Caesar is ordered to lend Trench his weapon in the sequel, he tells Trench that if he doesn't get his gun back he'll terminate his ass. During the credits, Trench is shown with the left half of his face in shadow, with a bright flash where his left eye is.
The Brazilian dub takes the allusion up a notch, Trench's answer is switched from "Not even in your dreams" to "Not even in the future."
When Billy runs straight up the mountainside in the sequel the whole team looks on in awe, with Gunnar in particular being impressed. Lee asks Barney if he could remember when he could do that and Barney says he can't. Sylvester Stallone's most famous character has a penchant for running triumphantly up tall inclines and in one instance ran up a mountain as preparation for kicking Dolph Lundgren's ass.
Harrison Fordhiding in the back seat of a truck with FORD spelled out in big capital letters in front. Also the Gunship Rescue he pulls off in the final battle is no doubt a reference to Han Solo, complete with making his entrance by blowing up an enemy chopper. Ford is also a certified fixed-wing and helicopter pilot in real life.
When Toll asks Doc why he was caught after springing him from the train in the opening of 3, the latter matter-of-factly replies, "Tax evasion". Wesley Snipes, who plays Doc, was found guilty and sentenced for the same thing in 2008.
Actor-Shared Background: We learn Gunnar has a degree in chemical enginering, which Dolph Lundgren also has. Almost all of Gunnar's backstory (Swedish, Fulbright Scholarship to MIT, leaving to become a bouncer, having a relationship with a celebrity he met as a bouncer) is taken from Lundgren's actual life.
All-Star Cast: The whole point of the film, though most of the "stars" are past their glory days.
Explicitly done by Stallone according to the other wiki. But not so much focused on the all-star part so much as the glory part. That is...
On his approach to casting, Stallone explained that he was looking particularly for actors who had not experienced recent significant success in film, saying: "I like using people that had a moment and then maybe have fallen on some hard times and give them another shot. So we’re always looking for actors like Michael Biehn and Michael Paré. I like those kinds of guys. Someone did it for me and I like to see if I can do it for them."
Also given a nod in the sequel, where the team watched new blood Billy The Kid running full-tilt up a slope and Christmas asks Ross:
"Remember when you could do that?"
Ascended Meme: The Expendables treat Chuck Norris's character with the same reverence as the internet gives Norris himself, to the point where they make their own Chuck Norris Fact.
Classically Trained Extra: Not in the usual sense. General Garza's two bodyguards, who look mind-boggingly similar to one another? Twin MMA fighters Antonio Rodrigo Nogueira and Antonio Rogerio Nogueira, who currently compete in the UFC alongside Randy Couture. Sadly, they're not seen in any hand-to-hand combat.
The Danza: Vilain's first name is Jean. Van Damme has said that he could return for the next movie as his identical twin brother, named Claude Vilain.
Doing It for the Art: Jean-Claude Van Damme refused to be in the first film without seeing a script first (which is why he wasn't in it), and even his role in the sequel was largely based on what he wanted to do with the character. In particular, the final fight between him and Stallone was originally going to be stunt-heavy involving a helicopter, but he insisted on a straight-up fist-fight because he knew his character needed to die in a very satisfactory way. Vilain even breaks the fourth wall during the fight when Ross struggles to get back up to his feet. "Is that all? The people want more for their money!"
B Movie action fans (and there were probably a few in the audience) will recognize Gary Daniels as The Brit. Some may even recognize him as Kenshiro from the live action adaptation of Fist of the North Star.
Many Dexter fans were surprised to see Angel Batista, one of the most consistently friendly, even-tempered, decent characters from that show, as a military dictator exploiting his island to fuel the drug trade.
Doc, much like his actor Wesley Snipes, is initially prevented from working with the Expendables due to a prison sentence.
This is why Mel Gibson plays the villain of the third film. After a recording of an anti-semetic drunken rant of his became public and the resulting public backlash damaged his career, it makes sense for him to play someone as loathsome as Stonebanks.
Similarly Named Works: Not to be confused with a 1989 Vietnam War movie, a 2000 made-for-TV movie, or two musical bands (one American and one New Zealand) with the same name.
Bruce Willis ad-libbed his jab at both Arnold and Sylvester about going down on each other; Stallone was initially disgusted, as revealed in commentary, but the line set the scene so well that it was kept.
Also, in the first film, the seaplane was supposed to be an unarmed escape vehicle, but in between filming, Stallone noticed one of the crew climbing out from the nose hatch, learned that it was accessed from inside the plane, and was immediately inspired to turn the seaplane into a gunship.
What Could Have Been: As mentioned in the description Seagal and Van Damme were offered roles but they turned them down due to problems with the producer and a dislike of his character, respectively. Also, Terry Crews' role was written with Wesley Snipes in mind. The role was almost filled by Forest Whitaker, but had to drop out due to scheduling conflicts. Kurt Russell and 50 Cent were offered parts but declined, and there are rumors that Chuck Norris was approached as well. IMDb claims Danny Trejo, Denis Leary and Alan "Wash" Tudyk were approached for certain roles that were written out when they had scheduling conflicts. Stallone wanted all of them if he could so we aren't sure if he wanted the universe to explode.