Well, it has been quite some time since the rest of the house has been completed. I finally added a bucket and rope to haul up stuff to the treehouse.
Real simple. A plastic shopping basket, a nylon rope, a pulley, a carabiner, an eyehook, and a long pole screwed onto the railing of the crow's nest. Then I added a cleat so that I can hold the basket in place and take the contents of the basket out.