Topshop. I must confess a slight addiction to red and black animal print but I think I'd be drawn to this regardless. The size means you can fit quite a bit of stuff in but not be lugging around unnecessary items. And it can do the important day to night multi-tasking which is especially handy if you've got lots of post-work drinks to go to in the run up to Christmas.
Oh and it's a little bit furry. That makes it like a small useful pet and who doesn't want to carry one of those around? You can get your own furry pet bag for £32.