Susan's mother is too houseproud to let Susan have any indoor pets. The family have a barn owl, Sophocles (her father named him), but he's only used for delivering letters and parcels and prefers to sleep outside. When Susan was younger she had a rabbit, but it wasn't very interested in being cuddled, and once it got out and dug up the garden. When it was killed by a fox Susan wasn't terribly upset.
Draco's family have an eagle owl which, like the Boneses' owl, is used only for delivering things and isn't considered a pet. Draco's never been very interested in the responsibility of caring for an animal - he used to steal borrow his mother's wand and use it to zap insects.
Romilda has a kitty! Mackie is a three and a half year old Bombay cat, who Romilda loves to cuddle and cosset... except for when she chews Romilda's books.