Comes free with the Remastered Version of The Last Of Us on PS4.
During Ellie and Riley's water gun fight in the department store, the shirt Ellie later wears at the beginning of the main game can be seen on one of the racks.
The fortune telling skull that you find in the Halloween store can be found as a treasure in Uncharted: The Lost Legacy. If examine the skull and read the fortune it gives you, you'll earn a trophy.
During the main game, the only character whose last name who is revealed is Jimmy Cooper (not counting the Firefly pendants), but if you get the Left Behind DLC, Riley's last name is revealed as Abel.
On May 12th, 2015 Left Behind was made available as its own standalone game on the PSN store for PS3 and PS4. This version comes with a two hour trial of the Factions multiplayer along with options to upgrade to the full game.