Nine bags, three sizes, one rule: it has to work on a Tuesday. I went through the new arrivals at Prada, Miu Miu, Isabel Marant and A.P.C. looking for the shapes that hold a laptop, a paperback and a set of keys without looking like luggage. What follows is the shortlist. A tote for the days you carry everything, a shoulder bag for the days you carry less, and a small bag for the evenings in between.

Structured enough to stand up on its own, roomy enough to forget what is inside. The Prada Route and Victoria Beckham's travel tote are the two I keep coming back to.

The shape that has quietly taken over. Worn high under the arm or slung long, a soft shoulder bag reads more considered than a crossbody and holds nearly as much.

Proof that a small bag can still be the loudest thing you own. Oscar de la Renta's crystal minaudiere and Miu Miu's Caprice clutch are for the nights that deserve them.

If you buy one thing here, make it the shape you are missing rather than the shape you already own three of. I learned that the expensive way.