Most duffel bags these days come with attached wheels, but if you still own one without wheels, then RonnK has an excellent tip for you. You don’t have to spend money on buying a new one because Instructables user RonnyK shows off a relatively simple way to add detachable wheels to nearly any bag you already own.
The process is very simple and will cost around $28.
All you have to do is add two velcro straps to the bottom of a duffel bag and strap the wheels around. This way you can easily remove them if you need to. Check out the Instructables post for the full step-by-step directions.