I like the idea of using sand in them because so many of the other things like rice would just be a mess if they got wet accidentally. You could always buy sand that is meant for a child's sand box at a building supply store or a garden center surely. Sand would be waterproof basically. Just set the pincushion some where warm or in the sunlight and let it dry naturally if it got wet. Just MHO
Brenda in Bama