“In the 1800s, cowboys and other manual laborers wore what was called “ready-to-wear” — second-hand clothing that had been discarded by the higher classes.
With few exceptions (such as military uniforms), new clothing was not mass produced back then. If you wanted an outfit, you went to a tailor, who measured you and custom-made the shirt, suit, trousers, coat, or whatever. If you out-grew your duds or just got tired of them, you might sell them to a second-hand (or ready-to-wear) store, where they would be bought by folks who needed inexpensive clothes for work.
That’s why you’d often see cowhands riding the range wearing a suit coat or vest and dress pants (rather than jeans). Also, many veterans continued to wear parts of their former uniforms for work.
By the way, did you ever wonder why chimney sweeps usually wore top hats and tuxedos? Well, the fancier the clothes were, the harder they were to re-sell… and the lower the second-hand price. Chimney soot was tough on clothes, so a black tux at a rock-bottom price was just what the sweep needed!” Cowboy Bob