These are the rules concerning portable alcoholic and non-alcoholic drinks:

The total amount of sold healing per reset must not exceed 3000 hp.
A maximum of 200 hp may be sold to one customer per reset. The cost
of such healing is calculated using this formula:

x = The amount of healing sold.

Cost = 4*x + x^2/10

This means that the more healing an item contains, the more expensive
it gets. These items must have a weight of at least 1.

The "strength" of the drink is equal to the amount of healing it makes to
the player when he eats it. Typically this strength should not exceed 50.

Use the file "obj/alco_drink" and "obj/soft_drink" for cloning and inherting
purposes. Please read the file find out which functions to call.

NB! "obj/alco_drink" should now be used instead of "obj/drink" for alcoholic
beverages. The older file remains only for backward-compatibility purposes
but it will be removed within a near future together with the connected call
"drink_alcohol()".

Examples of food and drink and an inn selling these items can be found in
/doc/examples/apple_pie.c and /doc/examples/inn.c.
Type "goto /doc/examples/inn" just to visit it.