My one cat likes plastic bags too. But she likes to lay on them. If it happens to be a big plastic bag from M's or something, she has been known to climb inside it and lay down. Weird cat!
She is also very possessive of her toys. I will go around picking up tons of cat toys off the floor to vaccuum. I throw them on the couch and she'll jump up and take them all down again. I swear she counts them or something!