What documents are required to cancel my work permit and extension of stay based on work in Thailand?

And the short answer is deleted. It is your work permit, your Extension of Stay stamped inside your passport. It is therefor your responsibility to take care. And what ever people will tell you: It is not the responsibility of the teachers council, the Ministry of Education, the fishery department, the cashier of or who ever they want to tell you. You and only you, but if it is not done as it should be done you will face the consequences and that must be reason enough to take care.

Seeing as you don't say where you are, this is just a general idea;

Usually you take your termination paperwork and your work permit to the Ministry of Labour, fill out the "cancel work permit" form they have there, turn in your work permit, then take your termination paperwork along with proof you canceled the work permit to the immigration office and cancel your extension.

IF you DO live in Phuket (Division 6) I think you're gonna hafta GO to the immigration office and check to see what documentation you need to take to them to cancel your extension. They are their own kingdom down there.