Kiddo never chose a blanket or toy that she needed for sleeping or comfort. Occasionally she would latch onto something for a day or two, but then that would fall out of vogue. For a while she was pretty attached to a stuffed sheep her great-grandma B gave her, but then for a while every time we'd come get her up we'd see that Agnes (the sheep) had been kicked out of bed. So, who knows. I think part of this is because when she was very young she started holding the collar of her onesie underneath her clothes, and that was her security item.
Given her new potty-trained status, Kiddo no longer wears onesies.
This has coincided with a new attachment to her jammies and onesies. If she finds a set that she is not wearing, she picks it up with joy, finds the collar, and settles in for a good thumb suck. She likes to have a set to hold when she takes her nap. It is not uncommon to return to her room at the end of the nap, and find that everything in the crib has been thrown out except the jammies and onesies. And two sets of jammies is better than one.
(And this picture is fabulous because she has a real smile on, not her smile for the camera. She's beautiful.)