Food of any kind will ignite a burst of heat-producing metabolic energy. Sugar-containing soft drinks will also help, although to a lesser degree. Alcohol is a vasodilator, which means it enlarges blood vessels and accelerates the loss of body heat. Do aggressive calisthenics before settling into the insulation and shelter. Sitting next to a large, sun-exposed rock or cliff face reflects the sun's heat directly to the body.
Snow is another great reflector.
Putting these techniques to work may provide life-saving warmth, and help to stave off hypothermia until help arrives.