The following is the complete Red Dead Redemption 2 100% checklist from the in-game progress menu. It reveals everything needed to reach 100% completion in RDR2. Reach 100% completion to get the "Best In The West" trophy.

Complete All Story Missions
10 Stranger Missions Strands
5 Bounties
25 Chance Encounters
1 Bushwhacked
6 Gang Hideouts
1 Points of Interest
9 Graves
144 Cigarette Cards
30 Dinosaur Bones
13 Legendary Fish
All Exotics Tasks for Algernon Wasp
10 Rock Carvings
All Hunting Requests from Train Stations
1 Treasure Hunter Chain
20 Dreamcatchers
50 Animals Discovered
10 Pieces of Equipment Obtained
10 Species of Fish Caught
6 Gangs Discovered (Automatic from Story)
10 Breeds of Horses Discovered
20 Types of Plants Collected
48 Different Types of Weapons Used
Reach Maximum Health, Stamina, and Dead Eye
Reach Horse Bonding Level 4
9 Challenges Completed
5 Shacks Found
5 Legendary Animals Killed
4 Table Games Played
5 Ranters, Ravers, and Campaigners interacted with
1 Bath Taken (at Hotel)
1 Show watched
1 Theater visited
6 Recipes crafted: Craft 1 cooking recipe, 1 tonic, 1 type of ammunition, 1 hunting item, 1 horse care item, and 1 weapon
4 Robberies: Coach Robbery, Home Robbery, Shop Robbery, Train Robbery