plant couch potatoes and evil magma peas in your garden. These plants give mega snacks at harvest, and also seeds to re-plant themselves when done. You can buy them in crown shop, or farm them from drops.
It will take a few days but gardening Couch Potatoes and Prickly Bear Cactus will yield rank 9 snacks. Gardening during KI special double reward gardening event will yield an abundant harvest of rank 9, 8 and 7 snacks!