I totally thought this would be a deep discussion on our dependency on oil, what the future holds, lol.
All fuel injected vehicles hate running out of fuel, they expect to be metering a liquid and produce incorrect mixtures when metering air. So far as I know, all electric fuel pumps in the gas tank use the gasoline as a coolant, and may overheat if you run low on petrol. If you run out of gasoline in a Gen 2 Prius, you need to add 3 gallons before the computers admit you have added any. (even if you don't run out, putting under 3 gallons may not show as adding any) If you try to start your Prius with no gas more than 3 time you will set a computer code that needs to be reset, at the dealer, after a tow. When you run out of gas, the computers quit being able to make the best choice between gas and electric and can run the High Voltage electric battery below the state of charge needed to start the engine. If this happen it needs a 201 Volt battery charger neither you nor the dealer own. The y will need to borrow one from Toyota regional after they tow your car to the dealer. If your spouse or worse your in laws are in the car when you run out of gas, expect 50 years of ridicule. Other that that, not much.
If it's an older car, expect that as it sucks up the last of the fuel in the tank that it will also pick up sediment of various sorts. It was a pre-fuel injected car, but it cost me 3 fuel filters and a carby clean-out before the fuel lines came clean again.
I know the gen2 Prius gave a non ignorable warning when the tank went empty with instructions to pull over. It was possible to continue driving at low speeds on the battery pack alone, but this risked drawing the charge down too low and damaging it.
