Even with how much is in the game, there's a huge amount of unused content within it as well as evidence of other features that were removed or changed during its development cycle. With sales of over 21.5 million units across multiple platforms, it was also ranked as the 3rd best-selling game of all time in 2010.
Grand Theft Auto: San Andreas, the third game in the Grand Theft Auto '3D' era, was originally released in 2004 to high acclaim from both fans and critics, ultimately becoming the best-selling game on PlayStation 2. There's still plenty to find in this game. This channel also has several videos on prerelease material and several poorly documented cut features.
GTAWiki is way ahead of us, more unused sounds and interiors and what not. Released in JP: January 25, 2007 (PlayStation 2), December 17, 2015 (PlayStation 3)