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Whether you run the heat in a car or not, the effect on gasoline/energy consumption is negligible. In "almost" all cars, the hot water that cools the engine also runs thru the heater core when you turn the dial to "red" to get some heat, so that is just that much less heat that the engine radiator has to remove ...in any case, insignificant effect on gasoline consumption.
Air conditioning is another matter altogether, since the air conditioner compressor runs from a pulley off the motor and consumes several horsepower when it's on and almost none when it's off; so don't run it unless you need/want airco since that consumes more fuel when running.
As for warming up before driving, once you get the motor started and running smoothly on its own, it will warm up faster if you actually drive rather than just sit there idling. But do not load up the motor until it is warmed up, so just drive moderately and accelerate slowly until the motor warms up.
One strange example of a car that does consume gasoline for heating the inside of the car is the VW 411/412. I had a 412 years ago, I think it was a 1973, and it had a gasoline fired heater for cabin heat. So you can actually hit a button and heat the inside of the car before even starting the motor; this heater burned gasoline from the gas tank and heated the inside air (indirectly in an air-to-air heat exchanger); in that case, heating did consume more gasoline ...weird car that was.
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