Healing Kit Dependency
A character cannot expend hit dice to recover hit points at the end of a short rest until someone expends the use of a healer’s kit. This represents bandaging the wound and applying alchemical salves to the damage. Only one use of the kit is expended regardless of how many hit dice the character chooses to spend. I like this variant. It explains how hit dice work in the context of the game world. There’s a degree of verisimilitude that the normal rules lack. And it gives the healer’s kit a beefier role in the game. I like that to. If a character runs out of hit dice to spend then a healer’s kit can be of no more use to him. This also makes sense to me, because presumably you can only benefit from so much medical attention. Yes, I like this variant a lot. It will take much to persuade me not to use it.
(explanation via https://iourn.wordpress.com/2015/03/08/variant-and-optional-rules-in-5th-edition-dd/#healerskitdependency)