Arktis do, or used to, a very very good little pack. Just one main compartment and no lid zippy pockets but folds down very very small indeed. Comfy and fits between bergan and sidepouch.
I bought it off an ex-gunner friend as with a few other bits and bobs, one being his old Berg crusader bergan. Which he had the front covered in a sort of elasticy mesh bungee thing, one daysack holder and ready to go.
Rocket packs as a daysack? Thanks but no thanks, good enough for your sandwiches and your flask - nowt else!