A guy on the news in Charlotte last night did the same thing. He said that he was on empty and gave it a try. He put in his card and filled his tank! Maybe they are smarter than you think?
Customer of mine "in the know" said that most stores shut down when they reach 1500/3000 gallons left. This is so that emergency vehicles can still get gas. His stores shut down at 2500 gallons.
"If" the breaker hasn't been thrown for the pumps you can still get gas.