12V Portable Car Heater
If your heater is busted, you don't necessarily need to pay those insanely high parts and labor fees. A 12V heater will plug into a cigarette lighter and heat your car even with the battery off. For best results, pick a convective heater.
Trap Heat From The Sun
Find seat covers in dark colors that will trap the heat from the sun during the day to help keep seats naturally warm. If you have leather seats, this will be an even greater necessity.
Get A Block Heater
Using a block heater, you can help your engine heat more quickly, and benefit from the engines activity to warm the cabin better than your broken heater. It uses an exterior source of electricity, so make sure you have a capable extension cord. Engine blocks cost anything from $50-$300, depending on the quality and brand.
Stow Emergency Layers
Sitting inside a cold car in extremely cold conditions can be uncomfortable and life threatening. To best heat yourself without the help of exterior heat generation, pack a few extra layers into your car to use your own body heat to accomplish the job.
Warm yourself up from the inside with hot drinks such as coffee, hot chocolate, or tea. Even if it is freezing around you, the inner warmth will make it more bearable.
Use Hand Warmers For More Than Hands
Spring may be a long way off but there is something to spring for if your extremities (or other parts of your body) are really biting the frost. Hand warmers come in many varieties including long lasting (and cheap!) chemical warmers and still effective, cheap and long lasting enclosed flame warmers. Stow a few in your glove compartment and put them under layers for lasting heat.
Get A Remote Start System
While idling your car will not heat the cabin up as fast as driving will, who wouldn't want to delay the inevitable trip through the cold to your car a bit longer to have some real relief when climbing into your vehicle? Remote start systems typically cost between $100-$300 depending on make and model.
Park In Garages
If you have the opportunity, park your car in a parking garage where there is a chance of more regulated temperatures. At the very least, your car will stay out of the snow for a bit if it's really coming down outside.
Install A Seat Warmer
Seat warmers don't have to come with your car any longer. For as low as $25, you can find many that plug in to a 12 V cigarette lighter. When all else fails many of these heaters can really pack a solid source into your backside, and can even act as a heated blanket.
Park Facing The Sun
If you can't afford to park inside a garage, park your car facing east, in a place where the morning sun hits. This will defrost your windows and heat your car by a few degrees, solving some otherwise annoying inconveniences.
Passengers? Huddle Up
If you are driving along with a few others, one of the easiest ways to warm up is to huddle up and use body heat to help along the process. If you are the driver in extreme conditions, you would be better suited stopping the car and finding heat rather than to continue driving.
Light A Candle
You may think a single candle wouldn't do much in a freezing cold environment, but the enclosed cabin of a car is actually a relatively insulatory space. One or two votive, tea, or potpurri candles--safely--lit within a coffee can will do wonders for raising your body temperature.
Insulate Unused Space
Any unsealed spots like doors or windows (especially if it's dark) will let cold air in quickly when a heating source breaks down. Blankets, cloth, newspapers, or other layered materials will prevent lots of air from seeping into your heated space.
Eat Spicy Foods
Certain foods will keep you warmed from the inside out. A diet loaded with peppers and warm chiles may just have you sweating even on a frigid day.
Think Warm Thoughts
Thinking happy thoughts worked in "Peter Pan" so why can't warm thoughts keep you warm? In all seriousness, this will actually help distract you from the fact that it is cold all around you, so give it a try!
Get It Fixed
Well, if all of these options just aren't cutting it, are draining your car battery faster than you can say "freezing," or you do have enough money and time to get your heater replaced, this is by far the best solution. Engines get hot, and all that heat could be in your car. So, you know, that's a thing.