Which would be preferred as a tag for unlockable content and items, unlockable or unlock?
I suggest unlockable for content, since unlock could then be used for "how do I unlock door x"
[unlockables] would probably be best. That way it does not, in fact, get confused with all matters of opening portals. It's unambiguous and well understood as a shorthand for unlockable content. That, and its easier to comprehend when seeing a question about "unlockables" than one about "unlock" (unlocking what?).