That's a great question, and it's one I hear often from new city dwellers or visitors! Generally, most public urban trash bins you find on streets, in parks, or at transit stations do not come with a liner provided. You are expected to deposit your trash directly into the bin. The responsibility for lining these large public containers falls to the city's sanitation department, which uses heavy-duty bags during the collection and cleaning process.
For your own home or apartment, however, it's a different story. The standard small or medium-sized kitchen trash cans sold for residential use typically do not include liners. You will almost always need to purchase trash bags separately to fit your specific bin. It's a good idea to check the product description or packaging when you buy a new can; sometimes they might include a small starter roll, but it's not the norm.
My top tip? Always have a spare box of liners on hand. It makes taking out the trash so much easier and helps keep your bin clean. For public bins, just focus on making sure your waste lands inside the container. Let's all do our part to keep our cities tidy