You can leave a COD blank, it just means free of charge.

So you can't sell back "special" Items?

No, you can sell back items bought for AU, once you open the Anka egg though you can't sell the resulting item back.

Darn it... because I bought around 5 Anka Eggs and I got two of each of the same item. ll'D

Often times you can swap duplicate egg items with other people who may have gotten extras of the ones you're missing. Just ask around a bit in the egg item discussion thread or in the market section of the forums.

Where is the egg discussion thread? I am having trouble finding it.

New item discussion threads can always be found in Trisphee Talk. The current egg item discussion thread is right here: http://trisphee.com/forums/showthread.php?t=20314