Q:

US Citizen living abroad, moving some personal/wife's stuff with out her presence

I am a US citizen living abroad after recently marrying a foreign national. My wife and I intend to move back to the USA after her green card is issued. I am preparing to take a trip back myself soon for work. We’ve begun to accumulate lots of things which we’d like to bring back to the USA. I figured beginning to move things now in carry on baggage instead of having to figure out air cargo in the future would make that easier.
My question involves customs/duty tax. I’m going to have 3 big suitcases/boxes full of things. One of those suitcases is for my personal things (clothes and normal travel stuff), one box is full of personal effects (wedding clothes for myself and my wife, everything used and entirely for us), and a third suitcase full of new things which are for our future home (which will likely surpass the $800 duty free exemption). 
I’d like to do things by the books in USA law and want to know how to document everything I’m bringing into the country so I can pay the required duty tax, and not have to spend hours at the airport having CBP look through my suitcases (as 1 person traveling with 2 large boxes and a large pelican case would probably raise some flag). 
How should I document my things, both used (personal effects) belonging to my wife and myself, and our new things to meet CBP requirements? 
One note - my wife won’t be traveling with me - will CBP allow her wedding clothes to still be considered my personal effects if she’s not there? Should I carry some evidence of our marriage?

A:

As a visitor to the US, even as a US citizen, I believe your exemption is $100, not $800.  But questions about how you should be classified based on your residence abroad belong more on Expatriates than here.  The actual questions you've asked here, however, do not appear to me to be off topic:

How should I document my things, both used (personal effects) belonging to my wife and myself, and our new things to meet CBP requirements?

Make an itemized list of everything that will be remaining in the US, along with its value.  Bring that with you when you travel, and present it with your customs declaration at the passport control desk.  Don't use an automated passport control kiosk if you can avoid it.
The way it's supposed to work is that you tell them about everything that's remaining in the US, and they tell you whether you have to pay duty.

will CBP allow [my wife's] wedding clothes to still be considered my personal effects if she’s not there?

I think not.  The definition of personal effects includes the phrase "articles intended and appropriate for the personal use of the nonresident while traveling."

Should I carry some evidence of our marriage?

It shouldn't be necessary.  It's seriously unlikely that a customs officer would challenge your ownership of the dress.  But it's possible, of course, and evidence of your marriage can't hurt.  A copy of your marriage certificate would surely be sufficient.

