You don't have to.
You certainly do not have to send in documentation like credit card statements, etc.
But since you are sending this in AFTER the CP200, (as a response), it IS considered a best practice to send in a simple listing of assets and liabilities
(which can be done by using the the insolvency worksheet foound about halfway down the website page here: http://www.irs.gov/publications/p4681/index.html
(a more usable, printable form can be found on page 8 of this document): Publication 4681
You can do this as an attachment to (page 2 of) of your explanation letter..
Say something to the effect of .. "The following was the value of my assets and liabilities at the time the debt was forgiven."
And certainly KEEP the copies of any and all documentation you can in the event of any audit.
You'll note that the form says "keep for your records," but I have seen this pre-empt a request for further documentation.
It cannot hurt.
Fianlly, if you simply send in the form with the notice and a letter of explanation you WILL be considered TAX
COMPLIANT, by responding to their request for an answer in a timely fashion.
But again, Ihave seen other tax prose advise the client t send in the worksheet simply to provide a more thorough answer.
This one is really your call.
If it were me, I would send in the worksheet, in an effort to provide a more thorough response.