When somebody collapses and stops breathing, make sure you remember how to do CPR. Just make sure you don't do it to some person who simply fainted, because you can be sued if you break a rib. Legal protection for Good Samaritans in the US is fading fast. Still, every citizen ought to know how to do this.
I have had to do it twice, once in a parking lot and once in church. One lived, one died.