Good clothes, quality shoes and a properly packed backpack are essential
Dress well and warmly! Choose good quality sturdy WINTER shoes. Don't underestimate headwear, throw on a neck warmer or scarf. Pack at least one extra layer of clothing - a sweater or sweatshirt.
And what else shouldn't be missing in your backpack when you head into the winter mountains? Definitely spare clothes (thermal shirt, gloves, hat, socks) first aid kit and headlamp. Food and plenty to drink. Bring a shoe grips or snowshoes.