bruce z..i sure wish someone would come up with a pocket container that you can boil water in.the last good kit was by that mountain rescue group who used a old fashion tire patch kit box.flat and easy to carry in a jacket pocket and had the basic gear for a overnight shelter and hot drink.all the survival sites are full of "make do's" that are the wrong shape or too heavy.
except for the gear in my PFD i'll have to admit i don't carry a real pocket kit anymore,just a few things in my pockets.

While it may not be a pocket-sized solution, how about a pouch-sized one such as a mini bread tin? Look at this: http://www.amazon.com/Set-Mini-Loaf-Pans-Inch/dp/B002UF8YCY .

Those could fit in a small MOLLE or similar pouch. There is a guy who built a "survival" kit out of one.

Standard Disclaimer, YMMV, IMHO

The problem of using tiny tins to boil, is that it takes for ever to boil any good amount of water. This mean if boiling is the main method of making water safe to drink, it would take up far too much time, effort and energy to do so. So you either need to use a bigger container or a alternative (purification tablets and bags).

I, too, have pondered this problem. My solution, living in the arid West,is to always place a cup of the right size around my ever present canteen, which is almost always a Nalgene or one liter drink bottle- 700 ml capacity, takes up almost no space, weighs about 2 oz. It also protects the bottom of the bottle.

my pocket kit: