As I've noted before, we're running out of stuff to add that's actually useful and not gimmicky.
You can thank Herculine for this one. Awhile back, she requested a new feature: the ability to have companions carry stuff, but not be able to actually equip it.
Other systems have used FOSE or the like in a convoluted manner to flag certain items as unequippable or such. I took an easier route of setting up a secondary container. An "invisible backpack", if you will.
In the future, I may approach Bunsaki for permission to use the Blackwolf backpacks for the mod. These are the ones used by Jessi and Kelsey. They're also the ones I use in my personal (non-uploaded) mods. These would ideally be equippable on command, like the collars, pip-boys, and such already in the equipment menu.
I haven't decided yet whether or not it's worth the trouble.
Either way; less rambling, more showy-telly.
There are now two inventory options under the equipment dialog menu. 'Personal' and 'Backpack'. Personal inventory is stuff the companion can use; things that are "on them". Items put in that container can be equipped, ammunition and weapons will be used, stims will be used, et cetera. The backpack is the storage container. Items in it are not directly accessible by the companion. They can't use armor/clothing, won't be able to equip weapons or use ammunition; won't use any chems that are in this container.
You can see here, Carrie's normal inventory. Notice the equipped dots next to some items.
Now observe the backpack contents:
Despite everything being equippable, nothing has been. This allows safe storage for important items; weapons you don't want knocked out of hands or ammunition used up. Outfits that don't fit in with the style you want the companion to have.
At present, on removing the companion from the party (through stay, go home, fire, or dead companion) the contents of the backpack are automatically dumped directly into the player's inventory. It's a bit counter-intuitive; most people would expect the items to go into the NPC inventory directly. Unfortunately, depending on what's in their "personal" inventory; this can very easily go over their carry capacity. This can cause problems here and there; risking even item loss, according to what I've read.
Since I didn't want the items to be unavailable until you hire on another companion to fill that slot; and since moving is still possible even for an overloaded player, going direct-to-you seemed to be the best option.
At present, the containers do not have a weight limit, nor a physical location you can reach to manually retrieve items. I'm considering changing tactics, to institute a weight limit, but I haven't been able to decide what manner. Should it be a straight limit (the aforementioned Blackwolf packs come in versions that allow extra carry capacity of 25 to 70 pounds, depending on which you equip); or a percentage of the companion's overall capacity; or even a match to their capacity - in effect doubling the amount they can carry?
The realism crowd is sure to bitch no matter how I do it; so I'm leaning towards a simple matching of capacity. Something to keep the container from being used as a bag of holding for thousands of items at a time.
If you've got an opinion on the carry weight restrictions, feel free to weigh in here.