Mary's favorite game, since she was a baby, has been something we call "Where's Mary?!" It can be played anywhere. All you need are hands, napkins, hand towels, wipes, blankets, a shirt. Pretty much anything you can cover at least your eyes with will work. Even a rug.
There she is!
And repeat. And repeat. And repeat. Until she either gets distracted or you get bored. You can probably guess which happens first!