Here is a list of all the Weapons, costumes, and achievements for Red Dead Redemption.

Pistols

Knife – Unlocked from the beginning

Cattleman Revolver – Unlocked from the beginning

Volcanic Pistol – Clear out Twin Rocks Hideout; for sale at Armadillo Gunsmith ($100)

Semi-automatic Pistol – Clear out Fort Mercer Hideout; for sale at the Escalera Gunsmith ($300)

High Power Pistol – Given to you during “Bear One Another’s Burden”

Mauser Pistol – For sale at the Blackwater Gunsmith ($800)

Schofield Revolver – Becomes available during “The Gunslinger’s Tragedy”

Double-Action Revolver – Clear out Tesoro Azul Hideout

Lemat Revolver – For sale at the Escalera Gunsmith after the Revolution ($1250)

Rifles

Repeater Carbine – Given during “New Friends, Old Problems”

Winchester Repeater – Clear out Tumbleweed Hideout or complete “Spare the Rod, Spoil the Bandit;” for sale at Armadillo Gunsmith ($350)

Henry Repeater – Clear Nosalida Hideout

Evans Repeater – For sale at Blackwater Gunsmith

Springfield Rifle – Clear Gaptooth Breach Hideout, given during “We Shall Be Together in Paradise;” for sale at Thieves’ Landing Gunsmith ($300)

Bolt Action Rifle – Given during "The Gates of Presidio;” for sale at Escalera Gunsmith ($750)

Buffalo Rifle – For sale at any Gunsmith shop when you become a level five Master Hunter ($475)

Sniper Rifles

Rolling Block Rifle – Given during “Empty Promises”

Carcano Rifle – For sale at Blackwater Gunsmith ($1100)

Shotguns

Double-barreled Shotgun – Given during “Spare the Rod, Spoil the Bandit;” for sale at Armadillo Gunsmith ($150)

Sawed-off Shotgun – Clear Pike’s Basin Hideout; for sale at Thieves’ Landing Gunsmith ($250)

Pump-action Shotgun – Give during “And the Truth Will Set You Free”

Semi-auto Shotgun – For sale at Escalera Gunsmith ($1000)

Projectiles

Dynamite – Given during “Father Abraham;” For sale at various stores

Throwing Knife – Given during “The Great Mexican Train Robbery;” for sale at various stores

Fire Bottle – Given during “The Demon Drink;” for sale at various stores

Lasso

Lasso – Given during “Wild Horses, Tamped Passions”

OUTFITS

Cowboy Outfit
Default Outfit of Marston.
Benefit: Nothing. Regular outfit for Marston.

Gentleman’s Attire
Join the Rockstar Social Club
Benefit: Play high stakes Poker games in Black Water.

Elegant Suit
Purchase the suit from the tailor in Thieves’ Landing.
Benefit: Allows you to cheat when playing Poker.

Duster Coat
Reach the “Peacemaker” Honor Rank.
Benefit: Protects Marston from the Trail Dust.

Mexican Poncho
Purchase any safe house in Mexico for $150.
Benefit: Nothing.

US Marshall Uniform
Infiltrate all US Gang hideouts in 1 day (in-game). Cannot be done until the mission, “The Last Enemy That Shall Be Destroyed” is completed.
Benefit: US Law or Marshals will not pursue you.

Rancher Clothing
Complete the mission, “The Outlaw’s Return”.
Benefit: Makes him look like a real rancher.

Legend of the West
Complete all of the challenges; Survivalist, Treasure Hunter, Sharpshooter, and Master Hunter.
Benefit: Increased Dead Eye ability.

Bureau Uniform
Get 100% completion.
Benefit: No one can touch you. Basically invincible to what Marston do.

Bollard Twins Outfit
Kill a Bollard Twin gang member and do the tasks required that can be found in the Outfit Menu.
Benefit: In the eyes of Bollard Twins Gang, you’re a friend.

US Army Outfit
Complete the “An Appointment Time” mission and do the tasks required that can be found in the Outfit Menu.
Benefit: Nothing.

Treasure Hunter Outfit
Kill a Treasure Hunter gang member to unlock the costume and do the tasks that are required which can be found in the Outfit Menu.
Benefit: In the eyes of a treasure hunter, you’re a friend.

Reyes’ Rebels Outfit
Complete the “An Appointed Time” mission and do the tasks required that can be found in the Outfit Menu.
Benefit: A disguise to make townspeople think you’re from the Reyes Rebels. Law in Mexico will not pursue you.

Bandito Outfit
Defeat a Bandido gang member and do the tasks required that can be found in the Outfit Menu.
Benefit: In the eyes of the Banditos and Outlaws in Mexico, you’re a friend.

DEADLY ASSASSIN
Available via Pre-order from participating retail stores.

To unlock the Deadly Assassin mission; do the following requirements:

- Find a chest in Coot’s Chapel near Armadillo
- Complete Twin Rocks Hideout
- Capture or Kill Moe van Bar Bounty found in Armadillo.
- Win a Duel in Armadillo
- Complete the stranger mission; “American Appetites”.

Achievements

Complete the following achievements to unlock Xbox Live Gamerscore points.

High Roller (10 points): Win over 2000 chips in a hand of Poker.

No Dice (10 points): Complete a game of Liar's Dice without losing a single die.

What About Hand Grenades? (10 points): Get a ringer in a game of Horseshoes.

Austin Overpowered (25 points): Complete Twin Rocks, Pike's Basin, and Gaptooth Breach Hideouts in Single Player.

Evil Spirits (25 points): Complete Tumbleweed and Tesoro Azul Hideouts in Single Player.

Instinto Asesino (25 points): Complete Fort Mercer and Nosalida Hideouts in Single Player.

Fightin' Around the World (5 points): Knock someone out in melee in every saloon in the game in Single Player.

Strange Things are Afoot (10 points): Complete a task for a Stranger.

People are Still Strange (25 points): Complete 15 tasks for Strangers.

Buckin' Awesome (10 points): Break the Kentucky Saddler, the American Standardbred, and the Hungarian Half-bred.

Clemency Pays (10 points): Capture a bounty alive.

Exquisite Taste (10 points): Purchase a rare weapon from a gunsmith.

Bearly Legal (5 points): Kill and skin 18 grizzly bears.

He Cleans Up Well! (10 points): Obtain the Elegant Suit.

More than a Fistful (10 points): Earn $10,000 in Single Player.

Frontiersman (20 points): Obtain Legendary rank in any Single Player Ambient Challenge.

The Gunslinger (5 points): Score a headshot on any enemy using Expert targeting mode.

Man of Honor / Chivalry's Dead (25 points): Attain highest Fame rank and either highest Honor rank or lowest Honor rank.

Gold Medal (25 points): Earn a Gold Medal Rank for a combat mission in Single Player.

On the Trail of de Vaca (10 points): Uncover every location on the map in Single Player.

Friends in High Places (10 points): Use a pardon letter with more than $5000 bounty in Single Player.

Redeemed (100 points): Attain 100% in the Single Player Game Completion stat.

Mowing Them Down (20 points): Kill 500 enemies with a mounted weapon in any game mode.

In a Hail of Bullets (20 points): Kill 500 enemies with any pistol or revolver in any game mode.

Long Arm of Marston (20 points): Kill 500 enemies with any rifle, repeater, or shotgun in any game mode.

Bullseye (20 points): Get 250 headshots in any game mode.

Unnatural Selection (20 points): Kill one of every animal species in the game in any game mode.

Have Gun Will Travel (20 points): Complete all Hideouts in a single public Free Roam session.

Slow on the Draw (10 points): Get 10 assists in a single Hideout in a public Free Roam session.

Hit the Trail (10 points): Get from Blackwater to Escalera before sundown in a public Free Roam session.

Posse Up! (10 points): Create a posse and get the maximum number of members.

The Quick and Everyone Else... (20 points): Be the top scoring player in any three consecutive FFA games in public matches.

How the West Was Won (20 points): Reach the top rank for multiplayer experience.

Go Team! (20 points): Be on the winning team for four consecutive victories in any team based game in public matches.

Most Wanted (10 points): Become a Public Enemy for 10 minutes and escape alive in a public Free Roam session.

Red Dead Rockstar (10 points): Kill a Rockstar or someone with this achievement in a public multiplayer match.

Additionally there are twelve secret achievements.

That Government Boy (10 points): Complete "Exodus in America".

Land of Opportunity (30 points): Complete "The Assault on Fort Mercer".

Sons of Mexico (40 points): Complete "The Gates of El Presidio".

No More Fancy Words (20 points): Complete "An Appointed Time".

A Savage Soul (10 points): Complete "At Home with Dutch".

The Benefits of Civilization (90 points): Complete "And the Truth Will Set You Free".

Into the Sunset (100 points): Complete "The Last Enemy That Shall Be Destroyed".

Nurture or Nature? (50 points): Complete "Remember My Family".

Dastardly (5 points): Place a hogtied woman on the train tracks, and witness her death by train.

Spurred to Victory (10 points): Complete 20 story missions without switching to a new horse at a hitching post.

Heading South on a White Bronco (5 points): Evade the US Marshals while riding the Hungarian Half-Bred horse in Single Player.

Manifest Destiny (5 points): Kill the last buffalo in the Great Plains in Single Player.