Postcards.  For some reason, it is difficult to find nice postcards in Harbin.  The Post Office is a good place to find good ones.  Many sell for 0.80RMB and include 0.80RMB postage already printed on them.  Additional postage will need to be affixed for international posting.  

Hypermarkets.  A Walmart is located in the Wanda market at the north end of the Zhongyang Dajie, just on the west side. It is a good location to purchase all varieties of Harbin and other beers; maotai liquors, and excellent hats with liners for cheap.  Beneath this Walmart are food markets.  There are also at least two other Walmarts and one Carrefour in the area.

Underground shopping markets.  A good local market can be found under the intersection to the northwest of St Sophia cathedral.   

Russian goods.  Sometimes, the premium Russian vodka Standard from St Petersburg can be found and purchased here, like in a seasonal ice bar on Zhongyang Dajie.  A famous heavy (~1kg) bread Lie Ba (列巴) or black bread (俄式黑面包) can be found at Huamei Western Food Restaurant 112 中央大街 or at the Harbin International Airport (HRB).