It's not hard to declutter (child of a hoarder here, so I'm well used to the mentality that people aren't as valuable as things).
If the house was on fire, would I
1. Run through the flames to save it
2. Pick it up on the way out the door
3. Be at risk of getting trapped behind it
4. Be at risk of tripping over it
5. Immediately have to replace it because I wouldn't be able to survive (literally) the next 24 hours without it
6. Immediately have to replace it because I wouldn't be able to access funds without it for at least a week or would get properly sick over the following month or so
7. Have to get an identical replacement within a fortnight
8. Have to get some sort of replacement in the next couple of months
9. Be a bit sad I didn't have it anymore
10. Be vaguely irritated when I next need that specific thing that I now have to get a new one.
If it's in category 1, 2, 5 or 6, it's a keeper. 7 and 8 if there's room for it and it's absolutely perfect. All other categories - skip it.
I've already identified those things - basically, if the house goes up, I upend the linen bin, drop in two cats, my phone, laptop and medication from the fridge and leave. If it's near the door and in its case, Mr D's guitar goes over my shoulder in the process (I don't feel particularly strongly about my own guitars or bass, but I know that's important to him - just not important enough for me to run back upstairs to get).
Everything else is just stuff.
If it's a controlled move, I'd take more, but I'd start with essentials like somewhere to sleep, somewhere to cook, things to wear that I actually wear or keep the new place/me warm, musical instruments, books, plants and cats. It would be choosing what to keep, not what to get rid of.