Model by Berk Gedik, from: https://sketchfab.com/3d-models/survival-guitar-backpack-low-poly-799f8c4511f84fab8c3f12887f7e6b36

Modified material assignment (Joey de Vries) for easier load in OpenGL model loading chapter, and renamed albedo to diffuse and metallic to specular to match non-PBR lighting setup.