The Good Sam laws are NOT as encompassing as suggested. The laws typically do NOT cover whether the suit is filed, just affects the likelihood of a liability if the suit goes through completely without being settled.
Good Sam laws in the US vary widely from state to state. Some are better than others. As noted, these laws do not prevent someone from trying to sue you. Depending on the particular state law they can, however, make it extremely unlikely for that suit to be successfull. To bring suit entails considerable expense for the plaintiff, and people are unlikely to do so without some hope of winning a large settlement.
In Alaska we are fortunate to have a very strong Good Sam law. So long as one remains withion ones level of training (whatever it is), it is very unlikely you will be sued. I am not aware of any cases of this happening in Alaska.
A couple of things one can do to make it even more unlikely is to keep your First Aid training current (do whatever refreshers are required by whatever certification you have). Keep copies of your current certification. And if you do provide emergency first aid assistance to someone, keep a detailed record of what you did, why you did it, and the circumstances under which you did it.