Berghaus Cubic 6+15

First it thinks it's a day pack

The concept hasn't changed, the sack part zips out complete with shoulder straps, but the construction is massively improved. The old Blitz always had a slightly flimsy, basic feel to it, but not any more. The Cubic uses tough Esdura fabric for a rough manly feel and improved water resistance, but it's also much better functionally.

Then it starts to eat itself

The 6-litre bum-bag section has a more substantial, stable belt with wing-shaped hip sections and decent, wicking padding, which means it performs as well as many specialised bum-bags. In an ideal world it'd also have some compression straps to stop the contents wobbling around.

And finally it's a bum bag. Cool...

The zip-out section gives an extra 15 litres of capacity and benefits massively from new, wider shoulder straps that support loads much better than the Blitz's rudimentary cheese wire versions ever did. It's actually all day useable as long as you don't try to carry too much weight high up and pack sensibly to compensate for the lack of padding.