Antarctica is truly one of those once-in-a-lifetime things. You won't regret it. And you will discover that it is nearly impossible to explain to someone who hasn't been there.
Let's see. Plan on layers. If your cruise doesn't supply them, waterproof pants are a must. My usual outfit for excursions was two layers of lightweight thermal pants under the rain pants. A thermal shirt, a t-shirt, and the heavy duty jacket supplied by the company. And I am someone who acutely feels the cold. I brought fleece pants to wear under the rain pants, but found them too hot.
I wore sock liners under heavy sick for expeditions. Washed the liners daily, because they dried fast.
The best thing I brought was a thingie called a neck gaiter. Wind can be a big issue. With this thing, you can breathe through the cloth, but not get clobbered by the wind.
You can rent gear if your cruise doesn't supply it.
For wandering around the ship, I wore one pair of thermals under knit pants, and a thermal top under a Tshirt. Be prepared, though, to grab something warmer when there is an announcement that something neat has just been spotted and you need to run out right now to look at the pod of orcas that just showed up..
You might get lucky. A crew member described the Drake Passage sea on our trip as "pathetic."
Sunglasses, definitely. For both sun and wind. Two pairs of gloves--one to wear and one to be drying. Sunscreen always.
You are about to go offline. If your ship has an internet connection, it will be a slow and very expensive satellite connection--just enough to tell people "Hi, I am here. Safe and sound. Amazing place. Talk to you later."
Binoculars. You want them. Bring a small, lightweight pair.
If you have a camera or something that is battery-powered, cold weather can deplete batteries in a burry, Bring spares.
When you are ashore, you can't leave anything. That means anything. If Mother Nature calls, you need to go back to the ship (and the crew will help you). Plan your coffee/tea consumption accordingly.
Penguins are really smelly.
