I use a discontinued product called Feeter Heaters. It is an insulated toe pouch with a pocket over the toe area for a small chemical heater. The heel is open but it has an elastic strap that slips over the heel to keep them on. You can wear regular boots while moving (instead of bulky pack boots) and then slip on the toe pouch when sitting. The pouches are way less bulky than the usual over boot. You could buy the Hot Mocs, cut off the heel portion and sew on elastic straps to reduce bulk. If the toe is warm the rest of the foot is not a problem.
