"I've been asked to get out of the car - do I have to?"  Yes, or you will likely be arrested.  If the officer pats you down, do not physically resist.  At this point, the officer has most likely determined you are under the influence.

The officer may then ask to search your vehicle.  You have the legal right to refuse the search if you choose.  The officer can not arrest you simply for refusing to consent to a search of your vehicle.  If the officer has probable cause to believe you have committed a crime, your car can be searched without your permission or a warrant.  However, if the officer improperly searches your vehicle, and finds evidence in the car, it can be excluded at trial.

Now that you are out of the car, the next phase in all likelihood are the field sobriety tests.  What happens next?  Stay tuned.