Photo: Courtesy of La Regale
The right size: Approximately 10 inches long (the size of a standard envelope), says Amanda Mull, handbag enthusiast and managing editor of PurseBlog.com.
The most common mistake: Choosing a too-petite style that barely fits a tube of lipstick and a credit card. Slip your essentials into the bag before you buy and make sure that you can easily snap it closed.
One to try: Chunky metal or colored zippers (seen on designer handbags like 3.1 Phillip Lim and Helmut Lang) accent a graphic shape—not to mention they'll keep everything inside secure.