I ship from Canada to Canada & USA via an ecommerce store front.
Here is my breakdown:
Box ($0.71) these are perfect sized, white ivory cardboard boxes
Custom Shipping Tape ($0.24) similar to Amazon's black custom tape, but my logo
Foam ($0.20) I use small pieces of foam strategically placed to immobilize some "combos"
Packing Slip ($0.39) Might sound weird, but I custom print nicer packing slips which fits nicely in the box, prevent the customer accidentally cutting through to the product on top, and have a nice design to them adding to a branded look/feel with the white box and branded tape.
So all together that is $1.54 per unit and I could probably get that closer to $1.00 with a more frugal approach, though I think little touches are worth it.