My child loves her sippy cups. Not one in particular, just in general. It usually doesn't matter what is in them, as long as it is not milk. She is not a big fan of milk. If she doesn't have a sippy, she'll take a cup (which she has gotten pretty good at drinking out of) or even a water bottle.
So, every night when she goes to bed, she wants her sippy. We put some water in her sippy for her, and that is what she sleeps with. She doesn't have a "blankie" or "luvie" or even a favorite stuffed animal. She has her sippy.
This is her at the beach this summer in her pack and play. Forget Minnie Mouse......I have my water bottle. Night Night.