I finally figured out what Mimi is doing when she brings junk in from the garage. She's hunting, and since there are no real creatures out there (at least I HOPE there are no real creatures out there) she brings me her kills in the form of: pieces of scrap wood, a large piece of cellophane off of a filter package, and assorted pieces of paper. (We have a really really junky messy garage) She brings them in with that 'look what I brought you for dinner' meow and drops them by the food dishes in the kitchen.
I praise her for being such a good little huntress.
She's such a little sweetie.