I've used a camera bag for years, to take all of my spare leads, strings, toolkit etc, to gigs. A bass player that I work with regularly turned up at a gig with one of these backpacks, and I was really impressed with the quality.
I have been using mine for a couple of months, and it has genuinely made my life so much easier. I carry everything from spare leads to microphones to a tablet (for charts).
This bag has numerous pockets and internal dividers to keep everything safe and organised. Like all mono cases, the quality is exceptional, including the zips and catches, and I can imagine having this bag for years.
These bags are expensive, but I did 190 gigs last year, so for me it's completely worth it.