Driving our homebuilt rig to Alaska....questions

I'd take the jack and spare(s) for sure. The sailboat would be up to you (obviously) but as stated above, there aren't a huge number of places to use it in Alaska, particularly if not equipped/willing for saltwater. There are sailboats up here, but most are a bit larger and focus on the saltwater...but one will see a few sails on the lakes when it's warm out.

I'd leave your milling machine...but take the kayak/canoe and bikes. Lots of opportunity to use both.