Hey fellow sparkies!
I just carry the tools I need in my carhartt bib overalls; usually a 5in1 screwdriver, strippers, volt pen, linesmans and wear a carhartt apron for wirenuts, etc. I carry a tool bag (CLC 81526 mentioned) and other required items on a tool cart which I wheel around on the job site.
After trying every combo of bags, leather or cordura, etc, my back hates it. My back loves doing the bib overall thing!