Get a slider from Australia Post - this way so you can make sure your book or dvd slides through ok in the 2cm gap. Sometimes you might neeed to 'pop a few bubbles' to get a DVD through ok

Free postage is a big no no if you have a $2 item that has be sent as parcel rates. For $8.60, your fees will gobble up any profit. i only use Free Postage when I can make the same profit if i dont use it

As for padded envelopes - buy in bulk! some sellers on eBay are way cheaper to buy from in bulk than if you but in bulk at the Post Office, some also offer free registered postage to you