I usually lug around my laptop and all other work-related stuff in an Phillip lim 3.1 bag. I love it but it's pretty heavy even without my laptop in and I'm sure it's not helping my posture at all. I'm therefore on the hunt for a rucksack to help my back. I'm looking for a black one that fits a standard laptop in. I will be travelling by foot between different offices in London so it would be great if it looked like a work one rather than a sporty/utility one as I'll be wearing fairly corporate clothes. Anyone got one that they'd recommend?