At this time all items are available on the equipment screen

You cannot "trade" between heroes as none of them horde items to themselves, but it goes into a common store for everyone use including regular units.

This could change although no one is asking for it at this time, but we are still early in development 

I appreciate both of you very quick replies.

I think this was a user error. I made another soverign surrender. When I looked at this soveriegn's equipment, there was a lot of items that my main sovereign could not equip. I saved the game, exited, and reloaded it. Then my main sovereign could indeed equip these other items.

Great, thank you!