Okay, so I had a road trip. Mostly highway, so I was able to do a bit of a test.
I have a 2013 LR4 HSE. With around 1,000 miles.
With a full tank I hit the road, driving for 339 miles on the trip meter before a fill up.
At 327 miles I was at "0 miles to empty" on the display, I continued to drive another 12 miles to the next highway rest stop.
If I do the math, figuring a 22.8 gallon tank, thats about 14.9mpg. The computer indicated 17.8mpg for the trip.
At fillup, I put in 20.6 gallons.
So it looks like I may have had around 22.8-20.6=2.2 gallons left, or another 30 or so miles at around 15mpg.
So, based on my non-scientifict study you might be able to get around 340-350 highway miles on a tank of gas. Even when the computer is indicating that you have "0 miles", you may have 10-20 or more to go before "true-empty".