Barrettes and hair ties have minds of their own, feel enslaved, and escape at first opportunity to a small beach resort on a small island off the coast of New Zealand. So those are a wash.
For gloves, hat, scarf: I think that the 1 pair and one of each, and then after that they come out of her allowance is a GRAND thing to institute this year. 100%. Do it. Be sure to warn her. Yep. She'll lose 'em. And yep. She'll complain about the cost of new ones (don't give her an option), and 1 will get you 20, after a few times, she'll start keeping track of them (unless she's adhd).
My uncle was an... adventurer... for lack of a better word. After his Phd, he scrapped hard sciences / astrophysics, and started making sports gear and traveled all over the world (mountian climbing, kyaking, skiing, etc) testing them. You see his products on photos of people in National Geographic. Our family (and his company, and many others who have copied him over the decades) has something known as "idiot cords". For kids this means that gloves have a long cord -about the width of a pinkie- sewn on each glove that goes all the way up one sleeve, across your shoulder, down the other sleeve, and is sewn on the opposite glove. Making them impossible for kids to lose. My grandmother started doing it. For adult gloves (and all the ones he made), it's a cord and toggle at the wrist of every glove that you put your hands through, tighten enough so they don't fall off when you take the glove off and let it dangle from your wrist, and then put your hand through the glove.
I'm a big fan of idiot cords.
I'm also adhd. Without them, I'd lose every glove I ever wear.