Old chair or sofa as @moocher suggested.
A charity shop briefcase can yield a surprising amount if you want something thicker or stiffer - I've rebuilt an elderly Brooks using a mould and several layers of wet formed briefcase leather, and made a vintage style saddle bag from a laptop bag. Catches zips fasteners and feet can also be re-used in many cases.
Old chair or sofa as @moocher suggested.
A charity shop briefcase can yield a surprising amount if you want something thicker or stiffer - I've rebuilt an elderly Brooks using a mould and several layers of wet formed briefcase leather, and made a vintage style saddle bag from a laptop bag. Catches zips fasteners and feet can also be re-used in many cases.