Getting rapped in the knuckles with a ruler. Trivial, and antiquated. But effective.
Caning in the penal system. It wasn't a picnic.
Bashing your shin into a low wooden table. Agony.
With perhaps the exception of the Eskimo, every culture on earth has traditions of defense with the stick. They formed armies of pikemen before swords arrived. Farm implements could not be outlawed, and so sticks were studied by Shaolin monks. The billyclub has been the sole force multiplier of police forces throughout history.
There are many ways to look at the three-foot stick.
A newbie can look at it as a striking weapon, a baseball bat, holding at one end and bashing into limbs. With proper coordination of the joints and a solid stick, the whiplike angular velocity can break boards, break bones. If targeted to a muscle area, the limb can go numb.
But aside from striking with the final six inches, you can also thrust with the tiny tip. If muscle and body weight are united, you are focusing hundreds of pounds of force in less than a square inch of body. Such force can stun, when targeted to the solar plexus, groin, short ribs, or kidney. More subtly, it can quickly change the entire balance equation of the opponent, adding much weight where it is not expected, at angles distinct from the vertical. Step on a foot to pin it, and bring weight to bear horizontally at the crease of the thigh, and the center of gravity goes beyond the balance line of the two feet. Kaboom.
The tip can push. The hook and horn can pull. Hooking a limb can let you pull in whichever direction you can shift your weight. The very tip of the hook, the horn, can pass behind an attacker and dig into his back or upper thigh, pulling him forward. If you can target the horn to a pressure point, the pull is more insistent.
When held horizontally between two hands, the shaft of the cane can block punches and kicks, regardless of the angle of attack. The motion of the attacker's limb adds to the impact of wood against bone or muscle. Precise targeting and strength are not necessary; you're carving out a wide area in space, supported by both hands, and can intercept and easily deflect an incoming limb.
If you're holding the stick horizontally between two hands, the wood acts as a fist-load when punching. Or you can punch with the hook or the tip, pushing with one arm and pulling with the other, to massive leverage without any impact of your flesh. And at any moment, one hand can release and push off, extending your range in a strike.
A stick can be used as a solid limb extension. It doubles arm's length, obviously, but it's not restricted to impact defenses. Instead of hooking your foot behind theirs to reduce movement, a stick can do the same, combining with a shoulder-push for a takedown. You can insert the stick between their arm and back, or between legs, reaching into locks that would not be accessible to hand or leg alone.
As a solid limb extension, we can go even further... the stick excels as a lever. If you control the fulcrum and points of contact, then you can precisely control the multiplification of force exerted by the lever. The added ability of a lever gives you great advantage in strength versus strength. Even better, you can pit the opponent's limbs against each other, by precisely weaving the solid stick between forearm, upperarm and back, or similar patterns on the body. It's almost like knot-tying -- you have to think ahead of where the stick can be inserted, on which side of each limb, but with practice I suspect that the principle of the lever has more importance than striking or thrusting ability alone.
In a different realm, the cane be used as a defensive device without any physical contact whatsoever. Large figure-8s or full-strength horizontal sweeps can clear an area -- define a space in which the opponent may not safely enter. A casual twirl of the cane while walking can catch the attention of a pedestrian and persuade them to not walk into you. A few restrained cane manipulations at a stoplight can deter other pedestrians from stopping right behind your elbow. The cane, in motion, can define space.
Every culture has used sticks. And there are many ways to use a stick. Many of the techniques of previous cultures are not appropriate today -- our goal is to stop violence, appropriately, and serious injury to the attacker today is realistically a loss for both parties. But the simple stick can be used for many purposes, rather easily, and (assuming you don't freeze up or panic) you can precisely tune the degree of force and risk of injury to the needs of the situation.
I don't think there's any one "right" way to use the stick. I see some using fencing techniques, other extending aikido techniques, some using hooking and jointlocks, others focusing on blocking or impact techniques.
A three-foot line, with a semicircle on the end... mathematically very simple, but capable of dramatic, and widely unsuspected, variation in the application of force.