In order to obtain a 100% completed game, the following tasks must be done.

Bounty Hunter (2%), which include eight in New Austin, eight in Mexico, and four in West Elizabeth (North).
Gang Hideouts (3.5%).
Jobs (2.5%), which include Nightwatch at MacFarlane's, Chuparosa, and Blackwater; and Horsebreaking at Ridgewood and Chuparosa. Note: You only need to do each location once.
Map locations (6%), which can be done by purchasing the maps from general stores or finding all the locations yourself.
Mini-games (3%), which include Poker, Blackjack, Five Finger Fillet, Horseshoes, Liars Dice, and Arm Wrestling. Note: You must make a profit on each game.
Outfits (4.5%), which include the Elegant Suit, Rancher, Poncho, Bollard Twins, Treasure Hunters, Banditos, Reyes' Rebels, U.S. Army, and U.S. Marshals.
Rank 10 challenges (4%), which include the ambient challenges Sharpshooter, Master Hunter, etc. Note: Reaching level 5 and 10 for each of them adds 1% to your total completion.
Rank 5 challenges (4%)
Rare weapons (2.5%), which include the , Mauser Pistol, Evans Repeater, LeMat Revolver, Semi-automatic Shotgun, and Carcano Rifle.
Safehouses (2%), which is done by purchasing all the buyable safehouses and renting both rentable ones for a total of thirteen.
Story missions (57%).
Stranger missions (9%), with the exception of "I Know You".