[mallrat]

If the coolant valve to the heater core will remain open with the engine off (i.e. cable operated rather than vacuum operated), NAPA has a nice inline heater with a pump to circulate the heated coolant, which splices into one of the heater hoses. IMO easier than removing a freeze plug and hoping the aftermarket piece holds up. Usually easier access in my experience.

Also, I like to keep a blanket or two in my vehicles during the winter, just in case. Could slide off the road, or the road could just get snow-drifted shut, etc.