Ive just been to Aldi & found a great product called a "Pour & Store" bag.
These are 240mm x 155mm size heavy-duty ziplock bags with 1 litre capacity that are designed to hold left over cooking sauces, oils etc & even left over meals.
Theyd make pretty good containers for FAKs & could be used as subload pouches for other kit.

The food grade plastic that theyre made of feels almost as tough as a platypus bladder & theyre dirt cheap, too.

I paid 89 pence for 8.

The product is the Poly-Lina Pour & Store

http://www.polylina.co.uk/pour&store.html

They seem similar to Glad freezer bags but the flat bottom feature is a bit different.
I will be looking to see what we have like them here.

I'm still interested in evaluating this product:

Aqua-Pouch

I love the the aqua pouch. I think I have 6 for testing various layouts of kits and methods of carry and have their aqua pouch plus kit as well - didn't test out the coffee filter/pre-filter support sheath combo yet.

Although they don't recommend it, you can fold it twice (from top to bottom, then widthwise and keep the zipper part on the outside of the fold) and its just a tad bigger then the DR PSK. I've had one of these pouches folded like I mentioned for about 6 months and test it about once every few months... Holding up good.

Kris

Just went to Dick's sports and picked up the Platypus 1L collapsible bottle. Just what I was looking for in a small package.
I have the oven bag and that should work fine, but I wanted a backup in addition to my regular aluminum bottles.

I have almost entirely gone to Platypus bottles in my kits. A pair of the liter size give you just the right size for using chemical water treatments and allows you to be drinking one and treating the second.

The larger models, roughly one and two gallons, are good for camp use and where you are using a bulk filter.

IMO these units are much better than most other options for PSK use. They blow away the condoms and breast milk bags.