I'm not into bags. I use a satchel which I love but I need another bag for occassionally carrying stuff to work like shoes, lunch and general random stuff which doesn't fit into my satchel. I'll still use my satchel as well. At the moment I'm using one of those fabric reusuable carrier bags. I think I'd probably prefer a bag with handles or handles and shoulder strap.
Budget about £50 but obviously less would be better.