I used to use briefcases to cart stuff to work and back, which did include my lunch of course. The I found that I was taking home work to do, leaving it in the briefcase and carting it back in the morning still not done.
So I bought a very slim leather briefcase that had a zip all around it and no handle. You had to carry it under your arm. It only could hold a small amount of paperwork, an amount that I could do at home without being put off by the quantity. I could still get my lunch in it.
So the secret of briefcases is it needs to be as slim as possible to restrict the amount of work you take home. Of course it was brown or rather tan, not black oh no.