I am very happy with my purchase of this SnugPak Response Pak from GlowGadgets (through Amazon UK).
As seen on the photos, this bag's multi-purpose adjustable straps allow it to be carried in a variety of configurations (either on yourself, or attached to some other piece of gear), and/or to carry extra stuff attached to its outside.
The 4 main zipped compartments hold enough stuff to free my pockets when I'm out on a 1-day field trip. There is also 1 very well concealed compartment in the back (flattened and closed by Velcro at both ends), big enough to hold a couple of passports and plane tickets. When all the compartments are full to capacity, the whole thing measures approx. 30x15x15 centimeters (12x6x6 inches); when empty, it weighs 400 grams (just under 1 pound).
All in all, this is a very versatile little bag, and I intend to use it in the waist pouch configuration, as a minimalist survival bag for emergencies (what Americans call a "bug out bag") which I will keep at all times in my car.
The only thing I would change in this bag would be make the synthetic fabric waterproof, and have the zippers opening at both ends - and this is the only reason I don't give it 5 stars...
I would also like to express my gratefulness publicly to Chris "Doc" Taylor at GlowGadgets (who hand-signed the order receipt) for the 2 free gifts (which would have cost me roughly 5£) that he shipped with this bag: 1 "BCB Fireball Flint & Striker with Compass" and 1 "Spork" (which you can also get from them right here, through Amazon UK). Thanks "Doc", you just got yourself a lifetime customer! :)