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.