As many as I can fit in my Safepacker.
Since I'm in winter carry mode now I'm carrying my P-12.45. I have 12 + 1 in the pistol. I have a pair of spare 12 rounders and a 14 round P-14 magazine which gives me 51 rounds of .45 ACP. I purchased the one P-14 magazine to see if it would fit in my P-12 which it does with a portion of the magazine below the grip.
I always have at least one spare magazine on me if I'm carrying a semi-auto pistol. At least a pair of Speedstrips or speed loaders if I'm carrying a .357 magnum revolver. Speedloaders if I'm carrying my .44 magnum as Bianchi unfortunately never produced .44 magnum Speedstrips.
Know the law; don't ask, don't tell.
NRA, NV & UT Certified Instructor; CT, FL, ME, NH, NV, OR & UT CCW Holder
Happy new 1984; 25 years behind schedule. Send lawyers, guns and money...the SHTF...