For several years I've been trying to find a bag big enough to hold all the essentials -- cards, cash, keys, sunglasses, lip balm, etc. -- but small enough to be thrown inside a larger bag when necessary. This was the fourth bag I tried and, though I've only had it for a few days, I am optimistic about this being The One.
To previous reviewer Karen: MP makes the bag that you describe! It's called the Urban Bag.