Coarse water softener salt, 50lbs bag for 3.99. Today I actually used a 50lbs bag of chicken feed as I had pulled my salt out and forgot to put it back in.
Bag of concrete, wrapped with house wrap and duct taped to keep from leaking.
I've used the house wrap and other convenient bagged products I've had around the house, like sand, corn or rock salt previously for different weight/dimensions.
A couple dumbbells and a soft 5 gallon water jug. The water jug is nice because A) I’ve always got plenty of water and B) If I get out too far or hurt something it’s easy to lighten the load
In past years I've used dumbbells wrapped in old coveralls, and water jugs of various sizes.
This year I'm comparing several different packs and trying to decide amongst them. I wanted a consistent, uniform, weight so I picked up several 40-pound bags of wood pellets. Works pretty well and I'm not worried about a bag springing a leak or anything.
Bag of cheap 25lb bag kitty litter for base. 5lb bags of rice for adding more is what I used for couple years. I got a brute force bag and been using that lately for base. It’s 45lbs. It’s nice cause it’s multi purpose