Just to be clear, the Mouser shipment I posted photos of above was a very unusual occurrence.
I order from them about every 4-6 weeks and normally the box is one of the 12x9x3 (inch) size. As I said before, best guess is that they ran out of the smaller size box and rather than delaying shipment just used a larger box.
I have been buying from Mouser for nearly 10 years, their customer service is top notch. If anyone has special requirements I recommend either calling them or sending an email. Odds are they'll be happy to work with you.
Sorry, accidentally deleted the post. There it is again.
Special requirements = Whatever you need.
If you want your stuff in the smallest possible box, just ask.