Best overall options: Whole corn, walnut shells, jasmine rice. I read that cherry pits are great for larger packs, but their heat doesn’t last in a small pack. Best scent: Cherry pits, jasmine rice, or walnut shells. If you choose a different filling, you can make it smell really nice by mixing in drops of essential oils, dried flowers, dried herbs, or cherry pits. Most pleasant calming feel: Flaxseed, whole corn, jasmine rice. Best heat retention: Whole corn, rice, wheat, walnut shells. Worst options: Buckwheat hulls (too expensive), clay beads or cherry pits (poor heat retention in a small pack), dried pinto beans or whole peas (beany smell), or flaxseed (even after a few heating's the oils were starting to smell a little rancid). Quick note, flaxseed would probably make an amazing cold pack if you kept it in the freezer.