Obviously, Pro and MMPKs make this much easier, but I think there are a couple of options if you don't have access to ArcGIS Pro.
Option 1:
Create a preplanned offline workflow in ArcGIS Online for your area (https://developers.arcgis.com/qt/offline-maps-scenes-and-data/tutorials/create-an-offline-map-area/)
and then download the map for offline use when the application starts up initially. The device can't be completely offline for this; you do have to let the user connect to network first so they can download the map area (https://developers.arcgis.com/qt/offline-maps-scenes-and-data/download-an-offline-map-ahead-of-time/)
Option 2:
If it's just the basemap that you want available offline, create tile packages (tpk) for the area you want and add them as your basemap in the MapView.
I think the general workflow to follow is:
1. Pick the map service for the basemap you want tiles for. World Imagery, Topographic
2. Export tiles from basemap using REST API
3. Add tpk to MapView's operational layers.
--------------------------------------------------
Application Developer, GeoMarvel