What can I do to prepare for this and still have access to the Internet? If you have any relevant experience from similar situations, please share!
It's possible you find a technical solution that works, but that's degraded and has very low bandwidth. Most of the WWW stops working in this scenario -- you hit serverside network timeouts and stuff. It might be worth figuring out in advance which websites are accessible under low-bandwidth conditions. Here's examples of the goal:
https://lite.cnn.com/en (7 kB -- with CSS and images blocked clientside)
https://lite.duckduckgo.com/lite/ (2.7 kB landing page; 6 kB result page)
Make a local copy of everything you have on the cloud (GMail, Google Docs, Google Photos, etc.)
If you store passwords in a cloud-based password manager, make a secure local copy.
Switch your sync solution from anything cloud-based to Syncthing.
Make sure you don't have anything critical stored on the phone (they may brick it).
If you rely on critical medical drugs, stockpile some (export restrictions are likely).
Finally, check the anti-censorship tech of Tor. They have something for places like Iran an China that have heavy firewalls and that helps circumvent them.
If internet cracks in two, there will be "El Paquete Semanal" on both sides.