Moonlight mead

Moonlight Mead is an ale that can be brewed with the Cooking skill at level 44 or higher, granting 380 experience. 4 Bittercap mushrooms are needed to make this, and it may be interesting to note that it has no Attack decrease, no Strength increase, and heals 5 Hitpoints. Also, the game remarks that "it tastes like something died in your mouth."

It can also be bought for 5 coins from Roavar in the Hair of the Dog Tavern, located in Canifis.

This drink is the cheapest 'food' in order for healing hitpoints. It will cost you at max 100gp to heal you fully, making it much cheaper then many common foods (such as Lobsters, Monkfish, Sharks etc.) The beer glasses can then be sold for a price, meaning you can profit from having a drink!