A tote bag is the perfect workweek and weekend carryall. It will fit all your essentials - exactly what you want from a bag on long days in the city.
If you're looking for a thrifty option, your best bet is this Neiman Marcus Tote Bag. It's a great product, while not very expensive. Why not also take a look at this AllSaints Tote Bag. It's an item you'll love which also won't break the bank. You might also want to consider this Trouve Tote Bag. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.