Except for the water-drinking reminder, nothing here is an absolute necesssity.

Drink water, early and often. If bringing a favorite water bottle will help, then do. If you have young kids who might drink more with a favorite cup, consider that. It's easy to forget to drink, but dehydration is like a hangover and then can turn serious.

Snacks to share (holiday gift food you might not want would work)
food for your room, maybe

If you colored a logo for the conference, maybe bring it (maybe send me a photo in advance)

Personal name tag holder (unless you want to use the plain string it comes with, or some of the other ribbons or strings that might be there). Maybe a favorite fancy shoelace, leather thong, gold chain, or a lanyard or fancy strap you already have. Maybe a diaper pin, or a brooch.

Electronics and paraphernalia
Camera, extra batteries, chargers
Phone, charger
Computer (if you do that sort of thing when travelling), cords, chargers
Lotion, lip balm, moisturizer, if you're used to a very humid climate.

Gloves, coat, cap in case it snows.
"Coat" doesn't need to be heavy like a Minnesota coat; layers of long sleeves and a hoodie or light jacket could be plenty, most likely. For snow play, waterproof gloves and ear-warmers would be good, but there's a Target store right by there, too.
Swimsuit for the hot tub or the nearby city pool.

Sunscreen and sunglasses for being outside any length of time. Anyone going skiing definitely needs sunscreen. People with sensitive eyes who usually wear shades in summer should pack those.