I have just modeled and textured a small cardboard box!
The modeling process was simple; I just took a cube, scaled and beveled it. Then after UV unwrapping, I painted the textures inside of Blender. Though I prefer texture painting with software such as Mudbox or Substance Painter, Blender was sufficient in this case.
After painting in the main cardboard texture, I used the Stencil brush to paint the tape, labels, and some dirt/stains. Then saved the texture and exported into Unity.
The next step would be to make a normal and/or spec map so the tape does not look quite so flat.