To activate Deluxe Edition you're going to need a key. To get this key follow theese steps:

• Open Ubisoft Connect
  
• Click on your profile picture/name in the top right corner
  
• Open account information
  
• Go to 'my games'
  
• Select Far Cry 3
  
• Click 'show key'

To activate the DLC follow theese steps:

• Open the game
  
• Go to options (in the main menu)
  
• Click on 'exclusive content'
  
• Activate your key

Note: you can't copy+paste into the game, so you have to type in the code.

The Far Cry 3 Deluxe Edition DLC includes:

• The Monkey Business Pack:
  Meet Hurk and his explosive bomb-carrying monkey in four heart-pounding missions and get two bonus ways to humiliate your friends in multiplayer.
  
  
• The Lost Expeditions:
  Discover the secrets of the island’s lost World War II ruins in two suspenseful action missions, and unlock the power of a shotgun in a one-handed flare gun in multiplayer.
  
  
• The Warrior Pack:
  Strike fear in your enemies with an exclusive dagger and unlock the tattoo editor in multiplayer.
  
  
• The Predator Pack:
  Hunt four ferocious animals with the M-700 Predator Rifle in single-player and silently kill opponents with the unlocked Predator Bow in multiplayer.
  
  
• The Survival Guide artbook:
  Discover unique artwork and insider information to help you survive the insanity of the island (PDF file).
  
  
• The game soundtrack

To get the survival guide PDF follow theese steps:

• Open Steam
  
• Right click on Far Cry 3
  
• Click 'properties'
  
• Go to 'local files'
  
• Click 'browse'
  
• The PDF will be there named 'FC3_Survival_Guide_Digital

You can learn different things that may come handy even in real life like morse coding, how to make different knots etc.

To get the soundtrack follow theese steps:

• Open Ubisoft Connect
  
• Go to 'games'
  
• Click on Far Cry 3
  
• Clock 'rewards'

You can download the official soundtrack of the game from here.
Also you can download some official wallpapers from here with different resolutions (zip file)