Ours all eat wood chips. Not sure if that is good or bad...they are also expensive depending on where you live (if you happen to live near a mill, I imagine they'd be free )

We use straw, both on ice and in the spring to give the mud some staying power. Cheap, and the horses don't "sample" it.

We dislike sand at all...because though we feed using buckets or tubs, two of ours prefer to knock their food onto the ground...we don't like to add anything inedible to our pasture.

Salt, I would say is a no...most of it has gross dyes or other chemicals in it.