The wife and I have been thinking about this and over the course of our discussions we come to the conclusion that because of our foundation as hikers we think of things differently.
As example we think about the weight of a sleeping bag as well as the insulating ablity, this doesn't help us give out good advice about car kits. Heavy bags that will do the job just fine never get our consideration because of the weight.
We also own a bunch of really gucci equipment because of the conditions we know we will encounter, because of our situation we think this gear is 'mandatory,' but it really isn't.
I don't know why we are hooked on the idea that they will have a car but lets assume that they do, It makes it easier to think about because weight is no longer a consideration
You can get really good cold weather bags for next to nothing (by comparison) if you don't mind what they weigh. I've noticed that I say things like this or follow my own though process without much justification and that isn't fair to you guys because I don't do a very good job of explaining my thought process.
The current theory is that it is easier and more effective to preserve the heat we make rather than warming our environment. From our stand point this has many added benefits, greatly reduced signature due to the lack of fire light and smoke, reduced exposer to our enviroment because you're not fetching wood, reduced exposer to burning youself or gear, no more smelling like smoke, no more acrid smoke in the eyes and lungs and it is by are and a way a lot easier to roll out a bag then chasing down dry wood. I know your idea was to bring fuel with you in the form of charcoal brickettes so some of those concerns are not your's but some are.
I well and truely believe that a good sleeping bag coupled with a tarp, bivy bag and ground pad is the way to stay warm. To this point everyone has said "buy, buy buy" and I know that sucks because you've got a jones to be creative and industrious and buying things doesn't slack that thirst. The reason for the "buy, buy buy" mentality is that some of these idems can't be made at the same quality by the average Joe but some can! Tarps involve very simple sewing (maybe glue or tape) and can be made with a higher quality than most can afford to buy and the same holds true for bivy bags.
If we look at tarps and bivy bags they are essentially the same thing but shaped differently. One hangs between you and the rain as a shield the other is wrapped around you. The material used serves the same purpose.. keeping you dry. Tyvek is a wonderfully light weight option that is very cost effective when compaired to the 'high tech' solution of sil-nylon. Neither one breaths worth a fuck and both are light weight. Gortex is another solution that in my opinion isn't worth the extra money as a tarp because you don't need a tarp to breath but in a bivy bag it is a wonderful materiel.
We haven't talked at all about condensation but if you crawl into an SOL bivy (best tech), trash bag (best value!), space blanket bivy (loudest) or just use a sheet of plastic (most useful) you will know all about it in short order! What happens is your hot warm breath (RvR) hits that cold plastic and loses it's ability to hold the moisture and bam.. cold wet plastic on your face. Not a good time.
Another area were you creativity can really shine is ground pads or puss pads as the door kickers like to call them. These are manditory equipment if you are even thinking about sleeping soundly. You dig, sleeping bags work because of the loft of the insulation i.e. isolated pockets of air. When you put your body weight on them they compress... which destroys the insulating value. To counter that we use Closed Cell Foam pads. They are cheap, water proof and indestructable which is nice. I use a thin USGI pad because it is wider and then a Wal-Mart Special because it is thick and if it is going to be cold I roll a piece of Reflextex over that to reflect my body heat back at me. There is no end to the configuration and modifications that folks have made to foam pads over the years. As example I use two because the dirt they are making these days is harder than the dirt of my youth
Some times I only roll the Wal-Mart pad down to the knees to keep me from rolling over in the night other times I put my pack under all that to raise my feet and calves to ease swelling.
I ramble and rave.. look up how to's on bivy bag construction and tarp making. There are some fantastic options from the Ray Way tarp tent to sil-nylon multi-cam unit and every wild contraption between. Fire is so 1800s man..
