You've certainly hit on an interesting and colourful question. There's a lot of anecdotal evidence and primary sources on this material, so I'll relate some of them (since they're fairly trustworthy). If you'd like additional readings on the material, I'd search through Stanley Crouch's book "Kansas City Lightning", which is about Charlie Parker. He was always a fairly poor gentleman, and there is a bit of information about how he procured his instruments and clothing.

To begin with, it would be helpful to note that the majority of bands in the early days of the swing bands used uniforms, which were paid for with subtractions from the musician's wages. In addition, depending on the musician, they may not have been poor at all. Coleman Hawkins, Duke Ellington, Count Basie, all of those men could afford nice cars and nice clothes. On the other hand, there are people like Charlie Parker, who continuously pawned his saxophone to pay for heroin, but the average touring musician of the time wouldn't have had a home or apartment to pay for, so they could afford to invest their earnings into instruments and clothing.

In New Orleans (I can't speak for other places) there was a tradition of service organizations and community groups providing instruments, and the earliest ragtime was often played with leftover civil war instrument (see A New History of Jazz - Alyn Shipton).

Clothing, when it wasn't uniforms, was often made at home - but maybe I'll ask /u/colevintage if they might know a bit more about that, rather than trespass beyond my expertise.

Does that mollify your curiosity?