Never used heatpads although we have a few around the house that were bought on Impulse. These are the ones that you re-energise by putting in hot water and when you want heat- you bend them. My wife used to work outside in all weathers and she used them as handwarmers.

But keeping wind and wet away from the feet works. Toe covers- better windproof shoes and windproof socks work. So does two pairs of socks with a plastic bag sandwiched between them. The other thing I have noticed is that socks containing cotton keep the feet cool--or cold in winter.