Piano / Soft: use Polenta or Sand for a soft and gentle shaker!
Mezzo Piano / Sharp: use Rice for a sound that is more pointy!
Mezzo Forte / Medium Loud: use Lentils or Corn for a rough and loud shaker!
Forte / Loud : use Beans for a harsh, loud rattling sound similar to maracas!
Source: https://www.youtube.com/watch?v=j8AcriiK5n0