Most men carry a pocket knife of some sort.  Originally these were usually two hand opening clasp knives.  People who wore suits all day usually had a small two blade knife called a pen knife, some were carried on pocket watch chains. These small knives were used to open maile,  clean fingernails, clean burned tobacco from pipe after smoking. Ranchers carried bigger knives usually with two to four blades like a Remington Bullet, or a trapper, or a three or four blade stockman knife. These had a main blade with a spear or clip point for general use. Then a smaller blade for castrating livestock called a Spey blade.  Another blade was the sheep’s foot blad which is used for precise cutting or carving and on the older knives a leather punch to repair broken bridles, belts, spurs etc.  also popular with boys were the old Boy Scout or camp style knives. These usually had a large main blade with a spear point, a can opener blade, a screwdriver blade, and a Lear punch or awl for making holes.  For hunters there were larger knives like the popular two blade folding hunters. These offered hunting knife size blades in a pocket knife for convenience. The main blade was conventional clip point for general cutting jobs and the second blade a skinning style with a curved point and belly.  These came with a leather belt sheath for carrying.  They were very popular with outdoorsmen and most major companies like Case, Ka Bar,  Camilleus, Buck, Schrade made them.  These old clasp knives were offered with different handle materials like stag (antler), bone, wood, mother of pearl, and plastic.  There were also single blade folding hunters also that just had the main clip or spear point blades.  One of the most popular of these is the Buck 110.  Originally lots of company offered one hand opening knives called springers, switchblade or push button knives.  When you are working and your are holding something and need your knife to cut it a one hand or assisted opening knife is handy. The Italians made a popular version during WW2 and the movies used them in gangster movies with the mob enforcer using them to stab people. Their version used as rear point thin blade that wasn’t very sharp as it was meant for puncturing more than a cutting tool.  They  were usually cheaply made stamped pieces with cow horn handles.  The Germans made a sturdier version with better materials  and good blades for cutting.  Some American companies imported them and carried them in their catalogues. These usually had India stag handles and are still around.  Now we have the popular flipper knives, a one bladed one hand opening knife that either uses a thumb stud or stud on back of the blade to start it to open then a flick of the wrist and gravity to finish opening it.  Some states outlawed switchblades due to the use by criminals so knife makers went to a legal torsion bar that assists the initial start by the thumb stud and quickly opens and locks the knife for your safety.  These are very popular now and most knife companies offer them in various styles, sizes, materials and price ranges.  These include Keyshawn, Gerber , Boker, Columbia River Knife And Tool (CRKT),   buck, Zero Tolerance,  Civivvi,  Cold Steel,  SOG,  and many others.  Another fairly new innovation is the out the front knife (OTF) knife where the blade does ing fold band into the handle but come straight out of the handle.  These usually cost a little more than the regular flippers as they Dre new technology.   They are offered by some of the same major players I mentioned before like Kershaw, Boker,  etc. these will be around $200 250 or so, where the flippers are less than a hundred for most but some are over a hundred like Zero Tolerance , Boker, etc depending on blade steel and handle material.  We can get into blade steels if you are interested.  Again not a expert or knif maker just a collector with years of experience trying to give a overview and not be boring.