Shipping packages is actually pretty environmentally friendly. The alternative would have been to drive a 2000 lb vehicle a couple of miles to pick up a 1 lb garment bag, making 0.05% of the total weight the payload. The other 99.95% of the fuel is going towards moving deadweight back and forth.
Shipping usually aims to hit anywhere from 10 - 90% payload, greatly increasing the efficiency by which carbon is used.
I did some rough back-of-the-envelope calculations a while back that showed driving to the grocery store used roughly as much carbon as shipping everything you were buying from New Zealand.