I have made scented rice bags or rice heat therapy bags several times as gifts. I use this tutorial.
Scented rice: In a glass Mason-type jar pour a teaspoon or slightly more of potpourri-type fragrance or essential oil, swirling the jar around to coat the insides. Add nearly a pound of uncooked, small grain rice. Place a coffee filter over the top and screw the lid on tightly. Shake well to coat the rice and place the jar on its side. Over the next few days, roll the jar frequently until the rice has taken up the scent of the oil. Cinnamon, apple, cloves, lemongrass, lavender, lilac, orange blossom, honeysuckle, rose, sandalwood, bergamot – the scent choice is yours.