My daughter was the ultimate "bag lady" as a toddler, so I can definitely relate to your situation. Here's what's happening developmentally: Around age 2, a budding self-awareness takes hold. What quickly follows, as most parents know, is a whole lot of "me" and "mine!" And, not surprisingly, toddlers simply like holding onto some of their own things. It's indeed possible that your toddler is doing this to cope with transitions and separations. If he can't have you in bed with him, he needs something else that is special to him.
So what to do? One idea is to give your son a child's backpack that's his to fill and carry. But once it's full (with trains, bears, blankets, etc.), no more treasures can come along. This approach will validate his needs while also setting limits -- a good strategy for dealing with many behaviors as your son grows up.
Copyright 2008. Used with permission from the March 2008 issue of American Baby magazine. Updated 2009