They covered a wide range of subject matter: sports, sentimental, comic, historical, floral, biographical, and - as shown in this Civil War veteran-related item from my collection: RISQUE (at least by 1890s standards, anyway)!
General: "Many A Battle Have I Fought Under That Flag."
Waitress: "No Sir, Not Under This Flag."
Read more about patent medicine trading cards:
UCLA - Introduction to a great online collection!
Miami University (Ohio) - Victorian Trade Card Collection
Harvard University - The 19th century American Trade Card