Power out but still connected for a while

When cruising by sail we had to of course always think about the source and the storage of power.  Engine, generator, solar panels, batteries, sun, diesel fuel were in the thinking.  When we began exploring America by Benz power never even came to mind.  But here I am with no power.  And I realize I have about two hours of phone and internet unless I go get in the car.  In two years of sailing never had that problem.  A plus for the travel trailer, you can be completely self sufficient?