The humble duffel remains the most versatile sort of bag you can buy. It is unsurpassed for utility and is equally capable whether you're using it as luggage on a long weekend trip or taking a change of clothes to the gym. I've got one that goes with me when I travel and one that serves as a sailing bag. This duffel bag is durably constructed and will not let you down.
The Port Canvas Company has been making canvas bags in Maine since 1968, first in Kennebunkport and now in Arundel. It remains a small, family-owned company, and each bag is still sewn entirely by one person (whose initials you'll find on the reverse of the label). If you find yourself in Maine you can stop by the Port Canvas factory and store and see how their bags are made.