[curiouscat]

I was wondering if any reaction of this sort exists:

A+B+...+H2O G1+G2+...Heat

where
A / B etc. are solids / liquids which are non-hazardous if ingested in small quantities
G1, G2 etc. are gases

My motivation was thinking  (quite a flight of fantasy!) of an alternative to a Flameless Ration Heater which is mostly based on this Rxn.:

Mg + 2H2O → Mg(OH)2 + H2 + heat

Alternatively, if the reaction is fast and substantially irreversible to completion we can relax the requirement for A / B being edible.

Wouldn't it be fun if you had an instant coffee pill that you could just drop into a cold cup of water?  

[manofohm]

Im not entirely sure how edible these components are but the decomposition of 29+% hydrogen peroxide gives off enough heat to boil water...(I am very famillier with this).

Many things can be used to decompose it the most edible thing that comes to mind are iodide salts but they usually offer a slower decomposition (relatively speaking) then others such as potassium permanganate or manganese dioxide. most metals and there salts actually will decompose H2O2 its just finding the right one for your job. The specific ones I have listed can all be bought as food grade items.