How do you make the amount of items a pet can have in its treasures increase? I want to start making a petpage and I need more item space.

You can use a Or you can get a random event that increases your pet's treasure chest.

Oh and also when using the pet zapper V2, there is a chance that the pet's treasure chest will be increased.

You could also get a but they're a rip off. xD

How many more items does it let you hold than the regular one?

The normal one give you 1-3, and that one gives you from 1-10. :D

Well that is a rip-off. You could only get 1!

That's kinda the point though, it's a gamble. It's either going to pay off or it isn't.

Do you know what shop they can be bought at?

User shops, or the Cash Shop for 500 credits. That's it. ;)

You can get the regular Magical Keepsake Box at the Millionaire Center, found in Centropolis for 150k sP.

Actually, the Multi-Compartment Keepsake Box gives your pet at least 10 extra spaces.

Also, when you get a for being here for two years, you can use it to give all your pets 10 extra slots. Of course you an also get a lot of other things from the box, but I used one of mine on the treasure chest slots.

Yeah, I thought so, but wasn't completely sure. xD

The simplest way would be the Magical Keepsake Box at the millionaire center in Centropolis.