In detail, this is what is included:
Care Package: a ULC pack containing the Doomsday Prepper Pack, American Muscle Pack, Outlaw Pack, Chaos Pack and Explosive Pack [Available 8th of May 2018]
Far Cry 3 Classic Edition (single player content only). With the Season Pass, get the game four weeks before it launches for a standalone purchase on the 26th of June 2018 on PlayStation 4 and Xbox One. PC players will receive the full version of Far Cry 3. For more information, visit this article.
All Season Pass holders will get access to Far Cry 3 on the 29th of May 2018.
[Available 5th of June 2018]
Lost on Mars: You'll leave Earth behind to battle arachnids on the Martian surface.
[Available 17th of July 2018]
Dead Living Zombies: Pits you against zombie hordes in a variety of B-movie scenarios.
[Available 28th of August 2018]
More information on the contents of the Season Pass can be found on the Ubisoft Blog or the official Far Cry 5 website.
Stay tuned for more on Far Cry 5's post-release content plans, including more details on the three separate adventures and the map editor.