I maintain a nostalgia budget. That is, I allow myself to keep a certain amount or mass or volume of items that are valuable to me (old photos, T-shirts, mementos from my family). This has made it far easier to get rid of things (especially things where I could just go buy another if I truly needed it).
How would I buy a notebook filled with my thoughts from 20 years ago, today?
A related approach I use with 'gear' is "can I buy another one if I really want one again?" (because I have a bit of GAS).
Of course I am economically privileged for being able approach the problem that way. Not everyone is.
:)