I was told to put Kitty Litter in my new speaker stands. Was he joking?

Look up Poly-Pellets weighted stuffing beads. They're widely available in craft stores and in various sizes.
These are the cleanest item I found for filling speaker stands.
They are good for adding mass, don't attract pests, have no issues with humidity, and probably dampen and/or prevent floor vibrations from getting to your gear.