455 Basic Fuel Advice Needed

When I was running all gasoline equipment I would normally refill everything at the end of the storm to have it ready for the next one. This would include a five gallon gas jug. I would also have all the vehicles topped off so extra gas was never a problem. I would like to be prepared with extra diesel fuel for the 455. After the full tank on the 455, how much spare diesel fuel do you guys keep around? Is 5 gallons enough? I have no idea how fast the 455 goes through fuel. Thanks.