@AngelaPreston I'm in the process of a large experiment wherein if something gets kept without there being a proper place for it (where it can be seen/used as intended), it has to be thoroughly inventoried (at least a photo or scan, and a record of where it is) -- with the idea that at some point we will all go through the various boxes and larger items one at a time and decide what should be done with them.
...of course, this is a slightly different problem than yours, because a large part of our inability to get rid of things is that although I am the organizer, there is stuff that isn't my purview to decide -- and yet everyone is ADHD on this bus so it's very difficult to get people to go through stuff on a dependable basis. (This is at least part of the point of the inventory system: I can generate a list of what needs to be gone through, and present the items one at a time... eventually... 
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