Your Inventory is where captchalogued items are kept. Items can aquired from Dungeons, the Item Catalogue, Consort Shops, and Alchemy. Additionally, you can Use, Read, Drop and Recycle items here.
How to expand Inventory. Edit
To expand the Inventory is simple: You get your Server Player to deploy Captchalogue Cards! it's in the SBURB Server under "Deploy" just select Captchalogue cards (it might say 1 grist type but don't worry!) some can spam click it to add multiple at a time. After the cards are deployed it'll be in the pick up section of your inventory when you Captchalogue the Captchalogue Cards click the use button and it should successfully expand your inventory.