Decide your use: topping for yogurt/smoothies (aim for crisp) or baking (aim for crunch that won’t turn soggy).
Choose the closest behavior: DIY toasted oats/nuts for best all-around match, crisp cereal for quick swaps, or nuts for a less-sweet crunch.
Measure by the listed ratio, then crush to the same size range as your granola so it bakes evenly.
If your swap is drier (nuts/oats), consider a small binder (melted honey/butter or oil) in baking to help it set; if it’s sweeter, reduce added sugar.
Rest after baking (or after mixing for toppings) so the substitute re-crisps before serving.