Do you carry extra fuel

I will give my specific scenario if it helps understand where i am coming from. I get 11 mpg pulling my camper with my 34 gallon tank I can go 350 miles or so and I can drive long distances without much issue. We travel a lot at night the kids sleep and my wife and I have some talking time. My wife had picked us out a Walmart to stop at 100 miles or so away. I had at least 150 miles till I was empty so I knew we were good. As we got closer she called to talk to the manager to get permission after talking to manager it was determined that they were 10 miles off the highway and that there another walmart 15 or so miles down the road that was right on the highway. I still thought we are good on fuel. Except for the fact my wife missed the exit inadvertently so we drove on past it and didn't realize it. Like I said in op the best laid plans. Now I am really concerned we finally see an exit with fuel. 2 stations both have diesel both are closed. It's after 1 in the morning. There was a State patrol at the second station and he told me the next exit had a truck stop and was open 24 hours and was 20 miles away. So I hit the highway drove very fuel efficient or as fuel efficient as you can be dragging 8000 lbs behind you. I made it and breathed a huge sigh of relief. So yes 5 gallons isn't as good as 100 gallon auxiliary tank but that night I would have paid a premium to have an extra 50 miles of fuel. I appreciate all the feed back hopefully this helps with my scenario.