Iv'e always found scrunched up pages of newspaper has done me the best over the years, when all the voids in the box are completely filled up with it it has the most impact absorption because the paper squashes in a lot, much more compared to bubble wrap, but obviously bubble wrap is very good too also.
If you've ever watched those documentaries on TV with reporters going into delivery/sorting depo's with secret cameras then you'll know how they handle packages, they're literally chucking them into metal containers and then deep into the backs of trucks like footballs to save time and effort. These workers are always on tight deadlines and try to rush through their parcels.
Just because you have a 'fragile' sticker on the package don't assume they will take notice of it, they don't always take time to check it over and read it and will still throw it around. So always assume your package is going to be thrown into a van and then have other packages thrown on top of your one too, then imagine how much protection that might need.
You don't own your toys, you only borrow them until you sell them or die!