The specialized gear you will need to bring will be minimal.
As a general rule, you need to dress in layers when you come to Alaska.
And don't forget your sunglasses! Even in wintertime, Alaska can have bright sunlight. Compounded with the snow it can be almost blinding.
Any specialized gear needed for a tour will most likely be provided by the tour company.
Other items to be sure to bring along are a camera and binoculars.