I don't know how many of you are NCIS fans, I am and I love it. The main character, Leroy Jethro Gibbs, played by Mark Harmon, is a tough and savvy repurposed Marine sniper who leads his team catching bad guy both domestic and foreign. He frequently teaches to the members of his team and applies a set of rules he has accumulated over his live experience. These rules aren't written down anywhere, except by fan on various web-sites, he just quotes them.
My favorite, and one I live by is rule number nine: "Never go anywhere without a knife". This is pretty good advice. As a paramedic / firefighter I had many occasions where a knife was a valuable and even lifesaver tool. For a Marine and NCIS crime fighter it is a back-up weapon and a formidable one with proper training.
As for me, I have had some training in my past. When I was a teen I studied and trained in Tae Quan Do and Jiu Jitsu. In which I learned a number of techniques to both defend against and offend with edged weapons. Even though I may be rusty, I would rather have the option than not. A good tactical knife beats the hell out of harsh language any day.
Here are a couple of other knifes I carry from time to time:
Top to Bottom; K-Bar Zombie Killer, Emerson CQC-7, Kershaw Spring assist Ken Onion design, Benchmade Griptilian.
So find yourself a good quality knife you like, and remember "Rule Number Nine".