Something simple I've been learning recently... I've been surprised it hadn't come up before.
I use the cane to exercise a lot... mostly stretching, a lot of pushing or pulling along the length of the stick, or wringing it out to build up the wrists, or using resistance at various angles to simulate lifting weights, and so on.
But exercising with two canes makes a lot of sense. A simple pushup has a lot more possible angles when each hand holds a cane a three to four feet ahead of your feet. It stresses more muscles too, because you've got to keep the canes upright... feel it all through the abdomen and oblique muscles, biceps as well as triceps. No need to go down on the floor... can still watch TV, in fact. The weight can shift back and forth from feet to hands... the angles between legs, trunk, arms, canes and floor can vary too. No need to go up and down twenty or fifty times, because there's enough degrees of freedom that you can just hold a position and slightly adjust to change the muscles stretches.
That "two canes forward" position is also useful for rowing and breaskstroke motions, where the cane can go off the vertical to the ground, and wrists can pivot. The two sides can go out-of-cycle with each other too... wrists moving in circles roughly parallel to the floor, right hand forward, then left hand forward, alternating. Lots of possibilities.
The two canes can be positioned behind the feet too, for squats and sitdowns. If the hands are braced against the body then it's easier than if the free canes must be stabilized by the wrists and forearms. I've also done some twisting work, with both canes places on one side of the body, but I'm not sure of the muscle groups here yet.
Pushups take advantage of double canes, but so does twirling. Why twirl with one cane when you can do both sides simultaneously? Both sides can work in tandem, or in alternation, or (I suspect) in different patterns simultaneously.
Figure-8s get very interesting with two sticks. I had seen people do it, but it took me awhile to figure out what was going on. It's probably easiest to start with a grip on the middle of the cane, so that the radius from the wrist is only eighteen inches or so. I found it easiest to start with slow Figure-8s 180 degrees out of phase, one wrist up and one wrist down, thumb sides of the canes looping to the left, then both looping to the right, following each other.
You've got four cane ends and two forearms to watch, but it comes with practice. All the standard Figure-8 variations can then come into play... arm positions, elbow movement, the angle between the two circles, size of circles, speed during different parts of the cycle.
Having the canes follow each other is the most straightforward to visualize, and after that mirror-imaging of the two hands is possible... thumb sides looping to the outside, then both looping to the inside. This is a little trickier for me, because the ends move through the body's centerline twice each cycle.
After that, the two hands can move off-cycle to each other, "broken rhythm", 90 degrees out of phase or whatever. Mixing in an extra loop on one side can switch from one phase rhythm to its opposite.
Anyway, two canes are a lot of fun to exercise with. I've seen Joe Robaina use them for pushups on the CaneMaster "Power Foundations" DVD, but in the "count of 10" style of doing many repetitions of a few motions, at set angles. Double-stick patterns and Figure-8s are done in the Filipino Sinawali style... like weaving a defensive wall in front of you. Considering the symmetrical benefits it offers, I'm surprised I haven't seen more discussion of it.