You've gotten some really good advice. I tend to sleep cold and have a 3/4 20 degree under quilt; I found my feet getting cold; just a small piece of the blue foam from Walmart will help a ton and it's also good for sitting on when you take a break. Just be sure not to trim it too small; better larger than you need than smaller than you need.
Also, I believe the hot water in a bottle would work but I think I'd just pick up some of those hand/foot warmers from the sporting good's department at Walmart. If your Walmart is a true super center they might even have the larger ones that are something like 3" by 6". A few of those between your thighs on the main artery will help.
Think multiple layers of non-cotton, not any lessor number of thick layers. A good stocking cap is a must and good wool socks. An extra pair of larger wool socks to pull over the first pair for sleeping will help.
It'll be a great adventure just watch it if you start feeling chilled; those conditions are ideal for the onset of hypothermia. If you're wet and cold hold up, setup camp, make a fire, get warm.