Warning, the following may contain spoilers.

The list spans both the single-player campaign and recently revealed , and will include objectives such as exploring the game world, securing gold medals in all extracurricular pastimes and hobbies, and modifying weapons and vehicles. A further 11 secret achievements remain under wraps, and are presumably tied to the game's narrative.

The list of alleged achievements is listed below:
Solid Gold, Baby! (50 points) - Earn 70 Gold Medals on Missions and Strangers and Freaks.
Career Criminal (100 points) - Attain 100% Game Completion.
San Andreas Sightseer (30 points) - Explore all of Los Santos and Blaine County.
All's Fare in Love and War (10 points) - Purchase Downtown Cab Co. and complete a private fare.
TP Industries Arms Race (10 points) - Purchase McKenzie Field Hangar and win the arms race.
Multi-Disciplined (30 points) - Attain a gold medal in all applicable hobbies and pastimes.
From Beyond the Stars (15 points) - Collect and return all spaceship parts.
A Mystery, Solved (15 points) - Solve the mystery of Leonora Johnson.
Waste Management (15 points) - Purchase the old dock and collect all nuclear waste.
Red Mist (20 points) - Complete all Rampages.
Show Off (30 points) - Complete all Stunt Jumps.
Kifflom! (30 points) - Complete your path to enlightenment#133; or not.
Three Man Army (20 points) - Survive 3 minutes on at least a 3 star Wanted Level with all three characters together off mission.
Out of Your Depth (5 points) - You're gonna need a bigger boat#133;
Altruist Acolyte (5 points) - Deliver an unsuspecting victim to the Altruist Cult.
A Lot of Cheddar (20 points) - Spend a total of $200 million across all three characters.
Trading Pure Alpha (10 points) - Make a profit over your total investments in the stock market.
Pimp My Sidearm (10 points) - Fully mod a weapon.
Wanted: Alive Or Alive (10 points) - Deliver a bail bond target alive.
Los Santos Customs (10 points) - Fully mod a vehicle.
Close Shave (20 points) - Complete all Under the Bridge and Knife Flight challenges.
Off the Plane (5 points) - GTA Online: Complete the Introduction.
Three-Bit Gangster (10 points) - GTA Online: Reach Rank 25.
Making Moves (30 points) - GTA Online: Reach Rank 50.
Above the Law (80 points) - GTA Online: Reach Rank 100.
Numero Uno (20 points) - GTA Online: Obtain first place in all competitive game types.
The Midnight Club (20 points) - GTA Online: Use custom vehicles to win 5 races.
Unnatural Selection (20 points) - GTA Online: Complete all 10 waves of a Survival.
Backseat Driver (10 points) - GTA Online: Direct a driver to 1st place as co-driver in Rally Mode.
Run Like The Wind (20 points) - GTA Online: Survive for a day with a Bounty on your head.
Clean Sweep (10 points) - GTA Online: Finish a Gang Attack without dying and kill at least 10 enemies.
Decorated (50 points) - GTA Online: Earn 30 Platinum Awards.
Stick Up Kid (10 points) - GTA Online: Hold up all 20 Stores.
Enjoy Your Stay (20 points) - GTA Online: Participate in everything Los Santos has to offer.
Crew Cut (5 points) - GTA Online: Complete a Job as a member of a Crew.
Full Refund (10 points) - GTA Online: Kill the thief that mugged you.
Dialling Digits (5 points) - GTA Online: Call for gang backup for the first time.
American Dream (10 points) - GTA Online: Own an Apartment, Garage and an Insured Vehicle.