The items Sage and Savory boost your maximum HP and TP by 5% respectively (10% with the Red varieties you obtain by using a Rune Bottle on them first). However, this boost doesn't account for the fact that Accessories can boost these stats. For example, if you have 1,000 HP, a Black Onyx equipped boosts this to 1,300. If you use a Red Sage without it equipped, you gain 100 HP - but with it equipped you gain 130. Thus, to maximize the boosts from the Sage and Savory items, take advantage of this calculation oversight by equipping your best HP/TP-boosting Accessories before you use the item.