On a typical day after work, I'm packed up and in the car in less than 20 minutes (usually more like 10-15).
I never notice any heat from the kb as I pack it away, and although I entertain the possibility that it CAN retain some heat, I haven't seen evidence of it personally.

Be that as it may ... I always leave everything in the car. Snow - ice - rain - heat whatever. I only remove items made of wood, like my guitars and clarinet. I DO take the laptop in in cold weather, but not in moderate conditions.

The only time I've seen trouble is in extreme heat situations when you leave an air-conditioned room after 5 hours and load the car in a parking lot that is 90+ degrees .... I've seem condensation form instantly. I try to let the temp stabalize before turning anything on, and it's always been OK. I am always early for work and time is usually on my side.

As for blankets? Can't hurt, but I'm still not convinced that they help. Good points made by all though.