For a short getaway or gym visit, a bag made of heavy-duty nylon or canvas won't rip (even when tossed into the underbelly of an airplane or bus) but is soft enough to stuff into a locker. A flexible fabric (like this lightweight nylon LeSportsac duffle) can be folded and stashed in a bigger suitcase on longer trips and opened up later to bring home souvenirs, says Glassman. Look for a version with both a top handle for holding just sneakers and a change of clothes, and a long, detachable strap that can be worn across the body to balance heavier loads when you're schlepping through an airport.
The right size: An overnighter roomy enough to hold an extra outfit, pajamas, toiletries and a pair of shoes. (Most airlines limit your carry-on to 45 linear inches—meaning your bag should be no bigger than 22" x 14" x 9").
The most common mistake: Buying a bag that's heavy when empty. Thick leathers stand up to being stuffed into the overhead compartment, but they add extra weight.
One to try: A striped style is easier to spot on the luggage carousel, and everyone from Tory Burch to Donna Karan sent stripes down their spring runways.
Next: Packing secrets from travel pros