Wow, so many responses. Thanks! (I need to join this great site!) Lots of good ideas. I'll try to expand on my strategy and ideas that led me to my current list.
First, I will be travelling by foot/snowshoe rather than by skis (which is a different category). Most racers use a pulk sled to take the weight and stress off of their backs and reduce any postholing by spreading the weight over more area. My pulk is snazzy, I'll post some pics sometime soon and a description of how I built it. Still needs some more testing though - this weeking I'll be out pulling and camping in the snow.
Having done long distance races in the past, at 15 hours I start to get a little bit mentally tired, by 24 hours I'm fried. Don't want to make mistakes out there and not be able to rewarm myself by pushing too long - so I plan on being conservative on this one, which means I will need to stop for two sleep breaks (maybe 1.5 hrs of sleep each time to recharge). At 37 miles there is access to a small store where I will be able to refill water and grab some calories. At about 67 miles is the only check point where there is a warm cabin, food and water. I may be able to make the 67 miles before sleeping, although if it is packed it may be better to sleep outside. The second half gets very hilly and will be slow going. I will stop for another sleep break somewhere along the way. Rather than carry a tremendous (and heavy) amount of water, I will use the stove to melt snow as I go. This will require me to stop every few hours and work in damp clothing. I will already be exhausted, probably a bit dehydrated (hopefully not too much) and underfed as well. With that combination in mind, I opted for a heavy coat and pants (and overboots) to put on before I start working.
Some racers suggest getting larger shoes and wearing more sock layers for foot warmth. I want to try using my normal shoes to help prevent blisters. Hardrocks do expand some so I will be able to layer a bit. I was under the impression that neoprene overbooties would not be enough insulation during my stops or very slow periods during the night, so I opted for the NEOS. Amazingly, my Hardrocks fit perfectly inside of them, with no spare room to slide around. Maybe they are too much. They are bulkier than I would like. I'll see if I can pick up some neoprene booties and test them out.
A light waterproof layer would make me feel safer, although I'm guessing at the temps I'll see any snow that falls will be really dry. I just treated my anorak so it's fairly water resistant. It is also somewhat light, 12oz including over-the-butt length and the newly added pit-zips.
What else? I'll have to go read more of the posts again... Thanks so much!