Endothermic and exothermic reactions

Consider the use of self-heating coffee cans when doing chemical reactions - how do they work, how hot can they get the coffee, safety features, can we build our own etc (I believe it's quicklime and water - except they colour the water red - cunning blighters - I may be wrong on that)

self-heating face-pack would be perfect for demonstrating an exothermic reaction - although the girls in my classes would have to try it on their hands to avoid messing up their make-up!

on the topic of exothermic reactions I thought about using self heating nescafe coffee cans. Does anybody know where yuo can buy these. The widget mixes the chemicals together and the exothermic reaction produces enough heat to heat up the coffee.

following on from that the american forces use something called a z-heater when they can't use stoves. Used by opening pouch, adding water + sachet of boil-in-bag food, close pouch, wait, eat.
They are available in this country from army surplus stores.