When you add a pair of regular price shoes to your shopping bag, a Puma backpack will also be automatically added to your order, no code required. The details say the choice of backpack is at the discretion of Puma, but the free backpack is showing up as the Deck Backpack ($30US value). This deal will be available until the 6th of September, but take advantage of this offer while supplies last. Sale items and Mongolian Shoe BBQ are excluded from this deal.
Remember, you also get free shipping with orders over $85US.
(P.S. Puma ship from the US, so watch out for possible customs)