Just set a difficulty level for a given bonus (depending on how accessible you want the benefit to be), and decide whether it will depend on specific ingredients (in which case it ends up being a lot like magical herbs). Even if it doesn't need specific items, you could still reduce the difficulty when working in a well stocked kitchen while raising it if you are cooking at a campfire with a very limited supply of ingredients.
If you want it to be more accessible than herbs, but still material-limited, you could use herbs but stretch their effect (e.g. one dose of the herb provides this lesser effect for up to six people).
