I recently came across a great jacket from Sherpa Adventure Gear. The Halka. At 10.6 ounces it's very well designed and is windproof, waterproof and breathable.
There was a rumor in the 2002 race that a race leader took only a Patagonia Dragonfly as a jacket. Remember, this was the route through the Wrangells and 2002 was the year of the July snowstorm. On Day 1 of the race, a blizzard dropped several feet of snow near the top of Cooper Pass. The Dragonfly is super lightweight at 3.1 ounces but mere mortals will probably want to take a jacket that provides a little more warmth, like the Halka. Besides, I don't think Patagonia is selling the Dragonfly anymore and Sherpa is a unique and innovative company.
I got my jacket on a recent trip out of state and there doesn't appear to be a local store in Alaska that carries their stuff so you'll have to do your homework. The quality gear should make it more than worth your time though.
An added bonus with this jacket is that it has the story of the jacket printed in Tibetan on the inside in case you're stuck in a tent somewhere and feel like learning another language.
Speaking of gear, don't forget about the REI Outlet store. You can often get screaming deals here on new lightweight gear.