An expandable vehicle system includes a drivable vehicle having a first propulsion system, a first set of wheels, and a first body supported by the first set of wheels. The first body at least substantially encloses and defines a first interior compartment. An extension unit has a second body and at least one wheel supporting the second body. The second body at least partially defines a second interior compartment. The first body is configured with a first attachment interface and the second body is configured with a second attachment interface. The first and second attachment interfaces are cooperatively configured to attach to one another such that the drivable vehicle is mechanically-coupled to the extension unit to form an expanded vehicle drivable by the drivable vehicle and with the first interior compartment contiguous with the second interior compartment.