Sodium bicarbonate (aka carb soda aka baking soda) - cheap, in the baking goods aisle at the supermarket. Use lots of it. Just sprinkle it in there, zip closed, leave for a week or so, repeat. Bulk it out with dry rice if you like. Vacuum it out when you're done, wipe out any residue with a damp cloth.

Nilodor is a (.au available) product in a little pump pack like the image above - it works amazingly well. A little harder to find; try a hardware superbarn. Febreeze is pretty amazing too.