A pistol from a major manufacturer, a quality 1911 or a Glock, which is what probably 90% of people use, in 9mm or more, with say 10 magazines (5 for carry, 5 for practice) a surefire type light with belt clip, a quality belt holster and at least one spare belt mounted mag carrier and a cleaning kit, eye protection and ear protection-preferably electronic. A Sig or Beretta, or even a Ruger or S&W auto would work also. edit-and a quality gunbelt
Trijicon type sights I am almost willing to put on the necessity list, along with two holsters, one regular belt holster and a 2nd iwb holster of some type.
An identical, spare pistol would be a good next purchase if you can afford it, but really a training class should be next after getting the basic equipment.
Now all I need to do is tack this on a church door