What do I need to do about my work permit and Non B visa before leaving Thailand?

You need to go and cancel your work permit and then take the documentation showing that to immigration to cancel your extension of stay based on a Non-B visa. You can normally do this a few days in advance with a letter from the company you work for. Obviously the last day you can do this is the day your work permit expires and that is the day you need to leave Thailand by. Whether you are ok coming back in on a visa exempt stamp (not VOA) will be up to the immigration officer you will stand in front of but if you have your ticket home in the time you will get stamped in for I don't see you will have a problem.

You can't pass a work permit to anyone. He will have to apply for a new one.

You will need to cancel both work permit and visa/extension the day you leave.

Just leaving the country will not cancel your extension.

Ok , YOU need to cancel your work permit and extension of stay before you bounce out and in. You can cancel a few days prior to your departure.