The disclosed computer-implemented method for updating containers may include (i) identifying an application container that is instantiated from a static application container image, (ii) identifying ancillary code that is designed to modify execution of the application executing in the application container, (iii) packaging the ancillary code into a data volume container image to be deployed to the host system that hosts the application container, (iv) discovering, by the application container, a data volume container instantiated from the data volume container image on the host system, and (v) modifying, by the application container, the execution of the application executing in the application container with the ancillary code, without modifying the static application container image, at least in part by instantiating the application container with a pointer to the location of the data volume container that contains the ancillary code. Various other methods, systems, and computer-readable media are also disclosed.