The following checklist reveals everything needed to reach 100% completion in Red Dead Redemption 2 (RDR2)

and earn the "Best In The West" trophy. It includes tasks related to story missions, stranger missions, bounties, encounters, hideouts, points of interest, graves, collectibles, hunting, treasure hunting, horse bonding, challenges, and more.

To reach 100% completion in RDR2, players need to:

Complete all story missions
Complete 10 stranger mission strands
Complete 5 bounties
Complete 25 chance encounters
Complete 1 bushwhacked mission
Clear 6 gang hideouts
Discover 1 point of interest
Discover 9 graves
Collect 144 cigarette cards
Discover 30 dinosaur bones
Catch 13 legendary fish
Complete all exotic tasks for Algernon Wasp
Discover 10 rock carvings
Complete all hunting requests from train stations
Complete 1 treasure hunter chain
Discover 20 dreamcatchers
Discover 50 animals
Obtain 10 pieces of equipment
Catch 10 species of fish
Discover 6 gangs (automatically from story)
Discover 10 breeds of horses
Collect 20 types of plants
Use 48 different types of weapons
Reach maximum health, stamina, and Dead Eye level
Reach horse bonding level 4
Complete 9 challenges
Discover 5 shacks
Kill 5 legendary animals
Play 4 table games
Interact with 5 ranters, ravers, and campaigners
Take 1 bath at a hotel
Watch 1 show
Visit 1 theater
Craft 1 cooking recipe, 1 tonic, 1 type of ammunition, 1 hunting item, 1 horse care item, and 1 weapon
Complete 4 robberies: Coach, Home, Shop, and Train Robbery
Outfits and clothing pieces can be found in general stores and tailors, with different options available in different towns. Trappers also offer special animal costumes that require players to skin the animals first.

To earn the "Artificial Intelligence" trophy, players must complete the "A Bright Bouncing Boy" Stranger mission questline given by Marco Dragic in Saint Denis. This quest is only available during the day, and players must have reached Chapter 4.

To earn the "Locked And Loaded" trophy, players can go to any gunsmith and change all the components of a weapon. This can be done at any gunsmith, such as the one in Valentine. Players can make a manual save before doing this and reload it afterwards to get their money back.

Other trophies that can be earned include:

"Legend of the West" (Platinum): Collect all trophies
"Lending a Hand" (Silver): Complete all optional Honor story missions
"Best in the West" (Gold): Attain 100% completion
"Gold Rush" (Silver): Earn 70 Gold Medals in Story missions
"Friends With Benefits" (Bronze): Complete a Companion Activity in each camp
"Hobby Horse" (Bronze): Play all mini games

In addition to the aforementioned trophies, there are several other trophies that players can earn in Red Dead Redemption 2. These include:

"Pouring Forth Oil" (Bronze): Participate in all optional Honorable and Dishonorable events related to the Oil Field in Chapter 4.
"Shootin' Iron" (Bronze): Achieve a headshot distance of over 250 meters with a long scoped rifle.
"A fool on command" (Bronze): Successfully perform a Fool's Gold headshot on an enemy wearing a fool's cap.
"Fightin' Around the World" (Silver): Knock out opponents in all different states in any fight.
"To The End" (Bronze): Reach the end of "American Venom" in any order.
"Most Wanted" (Gold): Capture or kill the most wanted criminals in each state in any order.
"Ducking the Devil" (Bronze): Successfully duck a total of 10 times in a row while in combat.
"Survivalist" (Gold): Discover 30 of the "Wilderness Survival Map" collecting locations.
"Be Prepared" (Silver): Craft every item in the game.
"The Gunslinger" (Bronze): Earn a combined kill count of 10 with a handgun and a throwing weapon.
By completing all these tasks, players can achieve 100% completion in RDR2 and earn the "Best In The West" trophy, along with all other trophies.

It's worth mentioning that this is a very difficult task, It takes much time, a lot of patience and some luck to be able to reach 100% completion and get all the trophies.