You could settle for a basic duffel bag or you could get the best of the best, e.g. Aer's Gym Duffel 2. This comprehensive and easy-to-organize bag features a whopping 37.4 liters of internal space across numerous compartments and pockets - including a 15.6" laptop pouch, a separate ventilated shoe compartment that fits up to a men's size 13, a quick-access front compartment for your EDC gear, and a generous main compartment. It's also built from durable water-resistant 1680D Cordura ballistic nylon and comes with both an adjustable shoulder strap and suitcase-style carry handles. Your gym gear is top notch; your bag should be, too.