Okay, I am not advocating dishonesty, BUT...
When I sent my M-bags, I packed everything in very well-sealed boxes and never was there any attempt to check the content of those boxes when I presented them at the post office. So for instance if a FEW CDs snuck their way into the boxes, no one would really know the difference. I'm just saying...but of course, for only a couple of CDs or whatever, you might as well just pack them!