I inherited my attachment to things from both my parents. I'm only 50, so don't have nearly as much items with attachments as they do. It has been quite a process for myself to find ways to let go. Downsizing can mean losing memories attached with items that no longer have space in the new life, nursing home, downsized apartment, or smaller space. One of the best pieces of advice I saw - that I've actually started acting on -
Just having the piece laying around won't help others remember or care about it when you are gone and those precious memories attached to those items will be gone when you or your memory is. Instead, take a picture, video, or many pictures...write a memory and why it is important. Create an album out of all of these memories. Some people start from scratch, others use online tools like Shutterfly to build them.
Even if flood, fire, etc occurs... those memories will be saved, but... the next generation may also understand and there is more of a chance they may decide to keep that memory alive also. This simple action can bring family together also, as putting the pictures and stories together can lead to memory building also.