People get cold extremities because heat is being lost from them faster than it's being replaced. There are two factors, the heat loss and the heat replacement.
Heat lost through the skin surface can be reduced in three ways.
1. Insulate. In was once common in winter for people to wrap their feet in rags and then pour water on the rags so that it would freeze. Ice is a pretty good insulator. There are better ways available to us now.
2. Reduce the surface area from which heat is lost. Put both feet (with or without boots, it's the same principle) in a large carrier bag stuffed with dry leaves for example. One bag for both feet is a lot better than one for each foot because you are more or less halving the surface area from which heat will be lost. This is why mittens are so much warmer than gloves and why grandma has that thing that looks like a stuffed cat which she puts both her feet in.
3. Reduce the temperature difference between the skin and the environment. You don't want the skin to be colder so you have to make the environment warmer. Put your feet somewhere warm, for example. You might want to take off your boots, for example if they're cold and wet, or likely to be damaged by heat. Incidentally wet boots (or any wet clothing) will have a much greater cooling effect than the same things do when dry because evaporating water takes a huge amount of heat. That's why you sweat, and why you have those wet sock things to put over milk bottles. If you can't get your feet warm enough when wearing wet boots, take them off and dry them out.
Heat replacement is through the blood stream, and there are two things to think about there.
1. The body has a thermostat. It controls the temperature of the vital organs primarily by using the blood stream as a coolant. When the body heats up it sends more blood to the extremities and skin surface in order to keep the vital organs from overheating. If that isn't enough then sweat is created to cool the skin (by the evaporation of water), which in turn cools the blood. Conversely, as the body cools down it will first stop sweating, then reduce the circulation to the extremities in order to keep the core temperature up in the safe zone. Reducing
any heat loss from the body or putting heat into the body
anywhere will help keep the extremities warmer because the body will carry on pumping heat (blood) around the extremities instead of reducing the flow. This is why a hat can help to keep your feet warm. A hot water bottle up your jumper may help too.
2. The circulation will artificially be reduced by things like wearing tight clothing, gloves and boots; sitting down and doing nothing for long periods; drinking alcohol etc.. Don't do those things if they cause problems. Some people have better circulation than others. If you're on the unfortunate end of the scale you will have to work harder to keep the extremities warm than others do. There isn't one single answer. Keeping fit through regular exercise can help a lot. Using power tools for example is notorious for causing problems with the circulation. A joiner who sometimes rides motorcycles with me has cold hands even in the summer, because his lifelong use of power tools has left him with 'vibration white finger'. In winter he has to go to quite extreme lengths to keep his hands warm, but it's doable.
Some people will try to hide the problem as if it's a personal defect. It isn't. It's just how we're made. You have to deal with it the best way you can.
I think that, er, wraps it up but if I missed anything please chip in.
/