This week I am test-driving a 2020 Ram 1500 with the "eco" diesel V6. Whatever it's "eco" merits, the thing can cover 1,000 miles on one full tank – 33 gallons of diesel. That's about twice the range of the typical gas-powered economy car and hundreds of miles farther than a hybrid car (more on that below). It is enough range to make it halfway across the country and leave the Golden Horde far, far behind. The Ram could go even farther, too – with a pair of 5 gallon jugs of diesel in the bed. Or convert the very convenient built-in "Ram boxes" on either side of the bed, which can probably hold five gallons each and could probably be plumbed directly into the main tank, bringing your range to more than 1,300 miles nonstop.
Assuming your bladder can go that long. (Men can deal with this exigency – without stopping – by keeping a couple of 2 liter soda bottles in the vehicle.)
A diesel-powered truck will also have the advantage of physical toughness – the ability take (and give) a hit, if that eventuality becomes actuality. If equipped with 4WD, they also have the ability to make their own road – which may be the difference between getting away and not.
A big truck also has lots of room – especially if it's a four-door cab. Some trucks have so much room – in the back – that two people can comfortably sleep back there. Another valuable feature in a Lord of the Flies scenario.
You might also want to consider a heavy-duty truck. Not that there's anything wrong with 1500s like the Ram "eco." It's that the 2500-series trucks are missing something. They don't have urea injection – and so you won't need to worry about DEF (diesel exhaust fluid) levels, which you will with all late-model 1500s. The 2500s don't have urea injection – yet – because they're not – yet – subject to the same emissions control regime as the 1500s.
There's another thing to consider, too. The Ram 2500 is available from the factory with a 50 gallon fuel tank. And its diesel is a V8 – with 850 ft.-lbs. of torque. That'll part the crowd, no problem.
Older diesel trucks – including 1500s – are free of the DEF gewgaw, too. And some of them will have simpler mechanical injection. Many were available with manual transmissions, which are preferable vs. automatics in an End Times scenario because they're much easier to fix in the field.
Another option is a diesel-powered car, which will also have the range and something else: