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

Expensive, but Atacama atabites are what I use. They are tiny bits of metal uniformly round and flat in shape. They are said to be better than sand and lock together once settled, creating a very dense damping medium for speaker stands. A bit hard to come by in the US, but can be had from UK dealers who ship to the US. Can sometimes be found on Ebay.

You can buy lead shot at Cabelas or Bass Pro. I used a mask (happened to have a few) and gloves, while filling with a funnel. A 25lbs bag was plenty for both stands. Music Direct sells a product by KEF that costs about $25.00 a bag. I believe it takes 2 bags per speaker stand. 

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.

Glass beads also available as well, if you feel you've got enough plastic, lead, sand, or kitty litter in your life already....

Kitty litter here is being used for the original intent, but it does hint @ a 'dual purpose' sub enclosure....they don't seem to mind bass lines... ;)

I built some stands in the first part of this year, as they are steel I was concerned with moisture embedding in kitty litter as it is hygroscopic. Steel and aluminum are both susceptible to corrosion/oxidation. I recall deciding that if budget is no concern, copper pellets or BBs would have been best. Steel shot that I have encountered, already has evidence of oxidation/rust so I would not introduce that into the stands. I spent an inordinate amount of time researching material and I decided on quartzite. If I recall correctly it is heavier than silica sand, it naturally breaks to a rough edge and therefor locks together really well once inside the stand columns. There is a company that produces crushed quartzite and it is labeled as Cherry Stone. I purchased a 50lb bag from Rural King for $7.99. It has worked out really well for me. The filling options are endless, sand blasting media, epoxy sealed aquarium gravel, or as mentioned above, glass beads. I would avoid kitty litter for sure.