@Jake *******
face it you're far from the first person here to get a 30 day extension, most immigration offices (seeing as you don't say what office of the 70+ ones here you're using) have copy shops nearby and the people manning them know exactly the copies to make,
as a rule you need
a passport sized photo (actually stated on the application as a 4X6 cm one, but most any will do)
a filled out TM7 application for extension (that you can down load and print front to back on ONE piece of paper or pick up there at the immigration office)
copies of
the data page of your passport
your entry stamp
your TM6 departure card
AND you might need a copy of the TM30 (that the hotel or the land lord of where you're staying was supposed to file with immigrations notifying them of a foreigner in residence there) BUT that is office specific and you might not need it
Those things and 1900baht get you an extension.
Post on a f/b group related to where you stay/live here in thailand asking what documents you need for an extension and you'll get people who've done it answer you