Encumbrance can help with the healer's kit. The bloody thing weighs three pounds and a character or party can only carry so much stuff (STR is a dump stat for some whole parties...). I know, a lot of campaigns don't really use encumbrance, but in this case it's helpful. When the party is going through them at the rate of one every other day that 50gp cost does (or at least should) start to feel prohibitive at the lowest levels. You know what's super easy too? Make them cost X where X is enough that the party doesn't want to buy them 6 to a pack like bon bons every time they hit a market.