hey, I was pleasantly surprised with the Merchandise. They have quite a bit, and it's better than Tokyo for merch too. They have a lot of items that say "Disneyland Hong Kong" on them so you'll be the envy of your friends!
One thing to keep in mind though, they don't really have accurate sizes, I guess due to the average sizes of people. So an XL shirt over there will barely fit someone who takes an L in North America.
Also, if you find at the end of your trip that you have some money left over, Disneyland has a pretty good store at Hong Kong Airport, so you can always pick up some more souvenirs in the terminal before your flight.