Don't loose sight of the basics. Keeping your head warm, will help
your feet. Keep your legs warm too. I wear heavy fleece pants that
zip down the side so I can unzip them (a bit) if I get too warm (or
have to pee). Remember, that as your body core cools, your peripheral
circulations is reduced which promotes cold tootsies. If you get cold
soaked on the way up (i.e. pee a lot) don't forget to hydrate on the
way down (very good article in Soaring, Dec 2007, Dan Johnson)

Chemical warmers will work IF your shoes/boots are getting O2. So
they will tend to work better on the top for your foot than the bottom
(where you are pressing on the rudder pedals all day). I have put them
in the tops of my running shoes while soaring and they help, but not
perfect.

Here is a cheep source for bulk quantities of them (Disclosu This
is a plug for my next door neighbor's company)
http://industrialsavings.com/Merchan...warmingpack s