Things you save not for their value as objects, but as symbols of a time, place, person, or feeling. Not to be confused with collections, say of matchbooks. Cheap, common objects long rendered impotent by time or removal from their native environment. Not the same as having a lot of junk and not remembering where it came from or what it was useful for, whenever it was useful.
These are items that serve as a key to locked closets in your memory, allowing you to access the smell of a graveyard, bits of conversation with lovers whose names you can't recall. Writing things down, taking a picture never fulfills this purpose quite the same way, unless you are a very talented writer or photographer. When you record a facsimile, you infect the moment with the nostalgia you begin to build the moment you decide it needs recording. A physical object has traits of its own that provide a link to sensual properties of the past you might otherwise forget. Writing or rendering something is a higher function, not a part of the world but above it, describing it. Objects taken from a moment are inconsequential parts of larger, changing pictures, but the signifigance we attribute to them can be greater than what words or pictures could ever describe.