It appears that they removed the ability to make and put custom items into your inventory. Or, maybe it is moved somewhere else. I already have custom items in some of my person's inventory! What do I do about making new ones now? 

This seems to be a side effect of the new container implementation in the character sheets, whether that is intentional or not would be a question for the devs. For the moment you can still add custom items, but only in the "Equipment" section of Manage Inventory. Hope this helps.

It also might be part of your Home options while in character creation.  There's a toggle switch for "Allow Homebrew".