Selling things to other photographers. Look at all the filters, bags, tripods, and other accessories that influencer photographers slap their names on and sell.
Also, pictures of potatoes, at least if you can get someone to pay 1 million dollars for one.
My favorite lens and the one that spends the most time on my camera are different lenses. My favorite by far is the 200mm f/2 but it's not always the most convenient lens to use since it requires a decent amount of space.
The 70-200 f/2.8 is the lens that spends the most time on my camera.