Indeed. Unfortunately in the deep desert, coffee in an open container evaporates too quickly to be useful for training...
Better to get your caffeinated anti-rhythmic buzz from your Keurig-branded, espresso-making stillsuit.
I think we all know that spice coffee is only brewed and enjoyed in the comfort of the sietch. When you're deep on the sand dunes, the only thing you are drinking is your own refiltered urine.
Although now I want to see a study on coffee spillage while riding Shai-Hulud...
Feel free to do the experiment, but attempting to walk without rhythm would, I imagine, lead to sudden jolts that would spill your coffee. Maybe if you were a carefully trained fremen and/or Christopher Walken.
The idea is to make a small change in pace, or stutter a step, every few steps. The big sloshing motions that end up spilling your coffee happen when you've taken many steps that re-inforce the sloshing motion, and a mis-timed step here and there counter that loop.
My friend was a waiter and told me the trick they used to keep from spilling the glasses they carried out was to waver the tray a bit to the left and right in a steady rhythm as they walked, which according to this probably disrupts the natural oscillation of the liquids and creates a new, more stable pattern.
Personally, oscillating the mug up and down in sync with my stride does a pretty good job mitigating left-right waves, but executing it well takes practice.
It should be subtitled: how to turn an afternoon's work into a paper in one of the lesser Physical Review journals plus fifteen minutes of internet fame (at current exchange rates equivalent to 300 nanoseconds of actual fame).
the researchers' "take home" advice is to look at what you're doing—so long as your mug isn't filled too high, a watched mug almost guarantees a clean run
This is the opposite of my experience, when I focus on the mug it seems harder to control the sloshing than if I just look at where I'm going and don't really pay attention to the mug.
As you walk don't hold the cup rigidly (making it move as you move) - let your hand bounce around, decouple the movement of the cup from the motion of your body.
"Walk without rythm, and you won't disturb the worm."