Australia Post Auspost eBay satchels Product Codes
3kg satchel code 39715
500g satchel code 39712
These codes are not for the prepaid satchels such as the Australia Post Plus White/Red/Blue coloured satchels, but rather the Australia Post ebay satchels.
By the way, make sure that you lodge each satchel at a post office, instruct the postal clerk to scan the item into the system, therefore you get a tracking event created when the item was sent ;)