Oh my goodness, your post just gave me a serious flashback! My DD6 did the exact same thing. Actually she still does, hee hee, though now she has lots of little treasure boxes to stash things in. She would even go to sleep with little trinkets clutched in her hand. One of her favorites at that age was this little plastic blue heart bead she found at a park, she called it "dirty blue heart" because it had lots of little scratches. I usually would offer to hold things for her if she needed two hands for something or encourage her to put them in her pockets, if she had any, but I never tried to break her of the habit. I always thought of it as a real interest of hers and and the way she'd hold onto things forever as a sign of her intensity and tenacity. She is a very strong willed child. I wouldn't worry too much about it, she will grow out of holding them in her hands and discover treasure boxes, purses, pockets etc.
