One thing about "space blankets": They don't breathe. They will trap your body moisture inside, so if you use one and then have to come you will be wet and will chill much more rapidly. Keeping that in mind, using them as a reflector for a fire and as a wind/rain break IS a good idea.

As for waving headlights about -- most cars today aren't built to permit it. But you CAN us jumper cables from the battery to get a spark to start a fire.