Greater Healing Potion

From the mechanical bosses through to Golem you will be drinking these, and the limit on your healing is never the potion itself but the sickness timer between sips. A Charm of Myths shortens that wait and effectively raises how much health you can recover over a long fight, which is why it earns an accessory slot well past the point its other effects matter.

Ingredients come out of the Hallow, so a sweep through hallowed caves is worth more than it looks. Boss bags and Mimics also hand them over in quantity, so if you are fighting anything at all you rarely need to farm on purpose. One thing to watch: unlike the tiers on either side of it, this one is not built from the potion below it, so an old stack of ordinary Healing Potions will never upgrade. Drink those or sell them.

A determined player can hoik past a Jungle Temple door before Plantera and loot the chests inside, which puts these in your hands well ahead of hardmode. It is a trick rather than a plan, but it exists if an early boss keeps killing you on the last sliver of health.