Develop a travel concierge service to help people when they miss their flights. Become a home, office, or life organizer for busy or disorganized people. Buy and sell used textbooks to university students. Start an online course in some quirky subject you know a lot about. Visit jumble sales and buy items to resell. Start an Airbnb, but for dogs, so their owners can travel and leave the dogs somewhere better than a kennel.
I created an “Every Day I’m Hustling” shirt and sold enough for the campaign to ship, but didn’t earn much on the experiment because of some not-very-effective Facebook advertising. Still, some opportunity here and a friend of mine is doing REALLY well with this. If you can create awesome designs and reach the right people with good Facebook targeting, Teespring can be very profitable.