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