Cabin in the Woods director Drew Goddard did a AmA on Reddit, and through the course of questions it came out that they nearly did an awesome DLC pack for Left 4 Dead 2. It sounds as if the download would’ve been really fleshed out, but it never came to be due to MGM going bankrupt and the movie being delayed. But how Goddard describes it, it’s something that would have been worth whatever they charged for it:

By the way — the game was gonna be amazing. You were gonna be able to play in both the upstairs “Cabin in the Woods” world and the downstairs “facility” world with all the monsters. Believe me, I HATE all video games based on movies, they always suck, but porting Cabin into Left For Dead felt like the right fit. It pains me that it didn’t happen.

A bit of Left 4 Dead did make it into the movie despite the DLC never happening. Valve allowed the filmmakers to put some Left 4 Dead monsters in the cubes at the end of the movie.