Read the instructions on the "guide" (page 51). I copied the following from the USCIS guide:
If you are applying for naturalization on the basis of marriage to a U.S. citizen, send the following four items:
1. Evidence that your
spouse has been a U.S. citizen for the last three years:
•
Birth certificate (if your spouse never lost citizenship since birth), or
• Naturalization certificate, or
• Certificate of Citizenship, or
• The inside of the front cover and signature page of your spouse’s current U.S. passport, or
• Form FS-240, “Report of Birth Abroad of a Citizen of the United States of America,” and
2. Your
current marriage certificate; and
3. Proof of termination of all prior marriages of your spouse-divorce decree(s), annulment(s), or death certificate(s); and
4. Documents referring to you and your spouse:
• Tax returns, bank accounts, leases, mortgages, or birth certificates of children,
or
• Internal Revenue Service (IRS)-certified copies of the income tax forms that you both filed for the past three years,
or
• An
IRS tax return transcript for the last three years.
so what I
sent with the application was what's highlighted in
red above.
about (4): I'm sure you CAN send other stuff listed in (4), but it says "OR" everywhere, so to make it simple, I just sent ONE of those things listed (IRS tax transcripts).
everything else (originals of tax returns/tax forms, leases, car titles, bank accounts, life insurance policies, bills, etc etc etc, whatever you think will help/what we talked about earlier ...) I
took to the interview (supporting evidence)
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NOTE ALSO: (this is again from the guide):
" All applicants must send the following three items with their N-400 application:
1. A photocopy of both sides of your Permanent Resident Card (formerly known as the Alien Registration Card or “Green Card”).
If you have lost the card, submit a photocopy of the receipt of your Form I-90, “Application to Replace Permanent Resident Card;” and
2. Two identical color photographs, with your name and “A-number” written lightly in pencil on the back of each photo. For details about
the photo requirements, see Part 5 of A Guide to Naturalization and the Form M-603 instructions distributed with your application.
Do not wear eyeglasses or earrings for the photo. If your religion requires you to wear a head covering, your facial features must
still be exposed in the photo for purposes of identification; and
3. A check or money order for the application fee and the biometric services fee for fingerprinting, as stated in the M-479, Current
Naturalization Fees enclosure in the Guide. (Applicants 75 years of age or older are exempted from fingerprinting and the biometrics
services fee). Write your “A-number” on the back of the check or money order.
Please download "The Guide" here, and read carefully pages around 50-58 or so, you'll see what you have to SEND and what you have to BRING to the interview.
http://www.uscis.gov/files/article/M-476.pdf
good teamwork helps, and believe me, it shows when you're finally confidently sitting before the IO.