When I was a kid my Grandpa always had a "Old Timer" pocket knife in his pocket. He used it for all types of things from cleaning his finger nails, to popping the lock on the bathroom door when it was stuck. He told me you should always have a pocket knife and this is something I believe to be true today.
They are a handy tool you can use to get yourself out of a jam or just make a few things easier. Over time the "Old Timer" was replaced by the famous "Swiss Army Knife" and MacGyver.
This guy could rebuild a Chevy 350 using only a "Swiss Army Knife". With all manner of configurations available, this wasn't just a pocket knife it was a "tool". From files and scissors, to a fork and spoon, the "Swiss Army Knife" greatly increased the versatility of the pocket knife from more than just cutting.
Now is the day of the multi-tools, first came the "Leatherman" but many were soon to follow. The tweezers of the "Swiss Army Knife" have been replaces with needle nose pliers, and with multiple screwdriver heads, punches, files and bottle openers a multi-tool truly is a toolbox in your pocket.
I have a few multi-tools, just so there is always one around. One for the truck, day pack, 4 wheeler and of course my belt. There isn't a day goes by I don't use my multi-tool and I would be lost without it. Below is a list of some of my favorite multi-tools:Leatherman Juice XE6 Multi Tool
Leatherman Leatherman makes a full range of multi-tools in different sizes to fit anyone's needs. From their "Super Tool 300" boasting a whopping 19 tools, to their key chain versions like the "Micra" measuring only 2.5 inches when closed. My favorite of the Leatherman line is probably the "Juice Xe6", small enough to fit in your pocked but it still has the tools to get you through most things.
Gerber Gerber followed in the foot steps of Leatherman and now makes some very impressive multi-tools. Gerber has taken the design of the multi-tool into new directions with some models like the "Multi-Plier 400" with one handed opening to more specialized tools like the "eFect Military Maintenance Tool" which gives you the tools needed to maintain your AR15, M16, and M4.