There are options for accessing material without the internet. These do require some form of access initially such as going offline somewhere such as School, work, or other hotspot.
Google Help - Use Google Drive files offline
Setup offline mode first by going to Google Drive in Chrome
Click Settings cog at top right, then Settings
Then select Offline
Then install the offline Chrome extension
Open the file you want offline from Google Drive
From the File menu - Make a copy if needed first, then select Make available offline
Alternative method:
While in Google Drive, right click file & make available offline
It will then show with an offline icon next to the file name.
Open Google Classroom
Go into your Class, then teachers post with the file
From the File menu - Make a copy if needed first, then select Make available offline
Google Help - Use Gmail offline
Open Gmail
Turn on offline mode by clicking the settings cog, then Settings
Then click offline, then Enable offline mail
leave the default settings then Save changes.
It will show a synchronise icon while it downloads the files to be offline
and once downloaded it will display a tick icon & show ready for offline when you hover the mouse over it