Whiskers and Paws in Horizon Plaza has everything you need.
YY Suen Pet shop in Wellington Street is handy if you work in central.. I have gone there to buy my dog's dry food and bought a few items over the years like dog bowls etc.
RmB 2/F 85-89 Wellington Street Khuan Ying Building.
I like her because she is also is very dedicated to animal rehoming.