Perhaps the best way to illustrate this is to think of how we make food crisp. When a potato slice is raw it is very flexible but when we bake it, it dries out and becomes firm and crisp, which means it breaks easily. Crunchy food is hard and makes a loud noise when you bite down on it. But, unlike something crisp, it might not break so easily. We think of carrots as crunchy. Just to confuse you, Kelloggs makes Crunchy Nut Cornflakes which are flakes of corn with crunchy bits of nuts baked into them.

Crunchy could describe nuts, crackers, granola cereal. (I like my cereal to be crunchy, not soggy.) It also describes the ground under certain conditions, like snowfall that has refrozen on top, or mud that has dried. (The snow crunches under their feet.) Crispy usually describes fried food like potato chips, chicken that has been battered and fried. (These chips are so crispy and salty.) Crisp describes an apple and also is used for cool weather. (Crisp apples are better than mealy apples. I went for a walk on a crisp winter morning.)