I have a 2013 F250 (26 gallon tank) and at first carried extra fuel cans, as suggested above. It was a pretty good, cheap way to extend my fuel range but inconvenient. You have to refill each can one at a time, then dump them in as needed. It got old after a while, especially on our 3 week trip through Utah.
Then I replaced the OEM tank with a Titan 51 gallon tank and it's *awesome*. No extra fuel cans to mess with and I can go 400 miles between refills and still have 10 gallons in the tank (I get 10 MPG).
So try the gas cans and if that works for you, great. You saved a bunch of money over adding/replacing a fuel tank. But if you have the budget, a replacement or auxiliary tank is a very nice luxury to have.