I don't see them mentioned and I don't know if they are in your regular clothes but spare socks, mitts and if you wear felt lined boots at least one spare pair of liners are very good things to have.
If there might be a problem drying them overnight then more are better.
Hands and feet get wet from snow as well as sweat and having a spare pair of boot liners and gloves might save you some frostbite.
You will want a dry pair of felts each day for sure,
You can dry the spares overnight, same with the mitts and mitt liners.
Having 2 sets of spares cover you in case you get a soaker.

You mention a folding shovel. Would this be an aluminum avalanche type shovel of one of the folding military styles.

You will want one of the aluminum shovels to move snow.

Snow shoe aren't needed as we do not venture off trail. Sleds trails are well packed beds of snow and are not a problem to physically walk on.

If both machines fail and walking isn't a viable option I'll get on the sat phone and call for help. If the scenario is life threatening the PLB will be activated.

I've done many trips like this in the past and (so far) have never spent the night out on the trail. So I'm looking to pack useful items in case my luck runs out. ninety miles a day is a conservative distance and areas of shelters are about twenty to thirty miles apart. Good note on staying hydrated to help avoid hypothermia. Thanks.

I wear Baffin snowmobiling boots and have a custom molded insole to my foot with hotronic m4 heaters. The m4's can give well over twelve hours of continuous operation but I only use them on an as needed basis. I've found that wearing liners insulate my feet from the heaters and am more comfortable without liners. I do bring plenty of warm socks though - one fresh pair per day plus one.

The folding shovel in my kit now is a basic metal camping folding shovel. It isn't the best but it better then using my hands. I also consider it a little heavy. I am interested in replacing it would something more suited for snow. Recommendations welcomed!

I hope so! Most of the items aren't bulky so I don't foresee an issue with a pack capacity of 50L plus I'll a large waist pack which will hold key items like the PLB and PFAK. The one item I see an issue with is a tarp so sourcing a lightweight and thin material will be important.

Not going off-trail is part of your plan, emergency kits are for the unexpected and deviations to the plan. $**t happens.

A lot of example here.

http://www.mec.ca/Products/product_listing.jsp?FOLDER%3C%3Efolder_id=2534374302725879&bmUID=1263063787436

I prefer one with a D handle and telescoping shaft. The D handle seems to work well with mitts on and the longer shaft makes it easier on my back.

I currently use the following model when backcountry skiing and winter camping.

http://www.mec.ca/Products/product_detail.jsp?PRODUCT%3C%3Eprd_id=845524442243587&FOLDER%3C%3Efolder_id=2534374302725879&bmUID=1263063791392

It does not have the long neck protruding from the shovel blade which makes it more packable but still has a very solid connection between the shaft and blade.

I agree.

Which is why I'm putting together a list of item for my cold weather kit.