The grounding straps that drag along behind the car (they still actually sell these? I haven't seen any in years) won't help with the zap you get when you get out of the car because it's you who's charged in that situation, not the car. The car itself is grounded through its tires. As you contact the car seat a fairly high-voltage static charge can build up, and you can take that charge with you when you get out. Wing is right, touching metal as you get out allows the charge to dissipate without that spark, or arc of discharge to the car.
Doing that, or using anti-static spray, seem to be the best ways to deal with it.