Regeneration Potion

The healing per tick is small and the total over a full duration is large, so this is wasted on a quick errand and excellent for anything that keeps you in combat for minutes at a time. Invasions are the obvious case: a goblin army or a pirate crew grinds you down through chip damage, and this covers most of that without ever touching a healing potion or its cooldown.

It runs on top of the Band of Regeneration rather than overlapping with it, and roughly doubles what the band alone gives you. Layer a Mushroom or the honey buff on top and the trickle gets fast enough to outpace weak enemies entirely, which is how people tank Blood Moons without healing. The ingredients are common enough that there is no reason to ration these. Brew a stack before any long fight and drink one on cooldown.