The memories you have of events and people from your past aren't held within the objects you hold onto, but they are a part of you, your past, your memories.

I think that if you want to hold onto keepsakes, but don't have much in the way of space to hold onto them, then perhaps take pictures of some of them, I'd start with the larger ones myself, and put the pictures into an album that you can easily store on a shelf. That way, whenever you're feeling nostalgic or particularly sentimental, you can leaf through the album and see those objects and remember why they are so special to you and who they are tied to.