I usually buy:
For the dogs: Toys & Treats
the cats: Toys & Treats
the rats: Toys(& stuff to go in thier cage to play with.. PVC pipe & perches), Hammocks, & Treats
the birds: toys, millet,... more toys. =]
the smaller rodents: usually just treats.
the fish: I usually don't get anything for the fish, but this year they're all getting upgrades on their tanks.