A modular autonomous cart assembly for transporting an item being shipped is described with a sensor-equipped mobility base that carries the item(s), a modular cart handle, a sensor-equipped modular mobile cart autonomy control module detachably attached to the modular handle, all sharing a modular common power and data transport bus. The autonomous controller of the modular control module is programmatically adapted operative to establish a secure connection to a wireless mobile courier node, locate the courier node and the cart assembly, receive sensor data from the base and control module sensors, generate steering and propulsion control commands using the locations and sensor data and send them to a controller on the mobility base so that the assembly can autonomously track and follow the current location of the courier node as the courier node moves and while maintaining a predetermined follow distance from the current location of the courier node.