The whole "put things into objects" interface is working. It's pretty effective, I think.
In the end, it wasn't too hard as I Just had to add another mode to the existing "equipment" UI. The equipment UI normally shows yourself on the left, and your gear on the right. However, this one shows the object in question on the left and your gear on the right. Everything works more or less the same. The objects you interact with can have rules (arbitrary) for putting things in them, and there is a simple callback when the contained objects change to let the object respond. So for instance, putting something into a box might cause it to close and lock tightly, or something like that.