I have a kind of three-tiered approach. I tote a fair bit of stuff back and forth to work, that I don't want to have to think about, but simply know it's there if I need it. I use a large messenger bag and there's enough room left over from the "stuff" to add a small purse, containing the walking around essentials, that I can pull out and use independently, say at lunchtime if I go out and don't want to hike everything around with me. Usually, that small purse is a waist pack, but if I want to be more dressy, I have a small leather shoulder bag that holds the critical items. These small bags are also the ones I use at other times when I'm not toting all the junk.