How do you make your pets Treasure Chest bigger?

Magical Keepsake Box from the Millionare Center (1-3 spots) Multi-Compartment Keepsake Box from the Cash Shop (10-15 spots) Random Event Zapper v2 Loyalty Box contains also a TC items that gives every Pet on your account +10 spots if I remember it correctly but this isn't an option until your account is two years old

That are the possibilities. C:

thank you