Bundles are saved to the OEM partition on the device.
A bundle is a zip file that contains the following:
bootanimation.zip—Boot animation located in the root directory
<user-space driver>.apk—User-space driver as a service (ACTION_BOOT_COMPLETED)
<main>.apk— (Required) The apk for the main entry point (ACTION_MAIN and CATEGORY_DEFAULT)
<sub>.apk—One of any number of apks that is launched by the main apk