I will be traveling to a Thai Island from my home in Chiang mai, I want send a couple boxes of supplies by post to lighten my travel load. Is it possible to just send the boxes to the local post office and claim them there on arrival?

The service that I see at the will-call window at my local post office is "poste restante" This page describes the service:

http://www.thailande.free.fr/en/postage.php

You would need the address and details of the PO on the island but I'm sure the PO in Chiang Mai could give you further details on the service.

yes but the main thing when you go to pick them up is have the tracking number.when i did it they didnt want id,passport, only thing they wanted was the tracking number

Yes, you can. To do so, ask your local post office as they will write the postal address destination where you will be able to claim your parcels.