I totally empathize with this.
When I was little (and still now actually) I had tons of little boxes and special hiding places to keep my special things. I had jewelry boxes that held notes from friends and trinkets from the fair and old jewelry of my grandmothers that I got to play with. As I got older and I started to have my own spaces I had a closet to put my shoe boxes full of things and shelves with albums for my pictures. When you have flat mates you end up using your bedroom as a place for all your things and then if you're lucky enough to live alone (which I have done once) you have a whole apt to put all of your special things in their special places that are just for you. There is something really special and important about having a place to put your things. A place that no one else will sully or trespass into.
After the session I mentioned above I went to the store and bought a bunch of art supplies. I came to our next session with a shoe box and tons of pens and paper and glue. We spent the next hour decorating that box until she felt that it was just right. I let her keep it in my office and told her she could put whatever she wanted in it (except dangerous or illegal things, I'm not insane) and I wouldn't look in it. Every time she came to see me I would give her a few minutes to add or take away or just peruse the items she kept there. Now I know that having a shoe box in my office didn't make being homeless any easier but it did make her feel like she had one little place of her own. Eventually she got a locker and then a small apt and she was able to put her shoe box there.
I think that we forget sometimes how important it is to have something that's ours alone. As adults with homes and families and room-mates we share so much of our space and forget about our little boxes of childhood. Maybe you should dig up that special box from when you were a kid or maybe it's time to have a craft day and make a new one.