@Jordan *******
You should bring the following for a 30 day extension of stay based on tourism:
1. Your passport and:
a. a copy of your data ("picture") page
b. a copy of your most recent visa (if you have one)
c. a copy of your most recent stamp
d. a copy of your departure card
2. [May not be asked at Bangkok Immigration] A TM30, filed in the immigration office.
3. The forms (each immigration office may have different forms, and want to use their special forms). For Bangkok Immigration, they are found at the "Files" section in the group.
4. 1x passport pictures
5. 1,900 THB.
You will also pay an overstay fine of 500THB a day, which should be 5,500 THB (500 THB times 11 days).