What do you guys do, and why? How many bullets are enough?
No one knows how many rounds it will take to stop any given threat, even if your shot placement if good. No one knows how many threats you will face at one time.
Try to carry "enough." No one can quantify that number, but if you don't have a reload, I would not consider that to be "enough."
Second, many malfunctions of self-loading pistols are going to be caused by the magazine. You need a spare in case that happens.