Here's a short list of what to take with you when you're ready to drop off your mail:
All of your mail (count your containers!).
Complete and send your online postage statement electronically or, if using hardcopy, bring your signed and dated postage statement(s).
Supporting documentation (your tally sheet or printouts from presort software).
A check or cash to cover any additional postage due (if your advance deposit account will not cover the cost of your
mailing, or if you've put
precanceled stamp or
metered or PC Postage indicia stamps on your mail). For precanceled stamp
or metered mailings, in lieu of a check, you can affix a meter strip to your postage statement to pay for the additional postage.
A check for your annual mailing fee (if you haven't already paid it).
If you want a copy of your postage statement for your records, then you'll need to bring two copies with you - the original to turn in with your mail, and the copy to keep.
The Postal Service uses this documentation to verify the postage prices you have claimed on your mail.