If I could only have three tools of preparedness and personal protection it would be a handgun, a blade, and a good light. The three pictured here are my favorites of each and represent my daily carry. In particular, this is a Glock 26 Gen 3, a Ka Bar TDI knife, and a Streamlight Protac 2Lx light.
There is a lot that you can accomplish with these three tools. The handgun should speak for itself: if you need one then it is the only tool that will do. A blade is similar in nature. While a devastating contact distance weapon, the knife is primarily an emergency cutting tool for myself, its role as a weapon is secondary. The light is necessary, as half of our time in this world is spend in darkness. It also makes a good impact weapon or smashing tool to break a window.
While there are other tools I absolutely believe in carrying (medical gear, a reload, etc…) these three tools are a given for any environment. Unless legally prohibited, I carry these items.