Instructions
Accumulate as much money as you can. Several outfits must be purchased, and they tend to be expensive. For example, the Elegant Suit can be purchased in the tailor's shop in Thieves' Landing. This suit gives Marston the ability to cheat in poker. The Mexican Poncho is obtained automatically when you purchase a safehouse in Mexico.
Complete main story missions and side quests. Many outfits are obtainable only by completing particular missions. For instance, the Reyes' Rebels Outfit can be purchased in the General Store in Escalera, but only once you have completed two of the Stranger side quests, Poppycock and Love is the Opiate. Pay attention to in-game prompts. They will alert you when new outfits become available.
Collect as many "Scraps" as you can. Scraps are parts of individual outfits that must be assembled to form complete outfits. Scraps are hidden throughout the game. Some are rewarded automatically for completing certain missions and side quests. For example, the Bandito Outfit consists of six Scraps. One is found in a chest in Sidewinder Gulch, one is rewarded automatically for completing the Night Watch side quest in Chuparosa, and the others are obtained by winning various mini-games and defeating certain enemies.