Well, the Humvee, provided you can find a gas station, has a much larger tank, so I presume the overall mileage (assuming you have a source to fill your whole tank) matches out pretty well. Plus, minivans aren't exactly all terrain vehicles, nor are the very sporty: the one I have to drive on occasion can't take most turns at much more than 20mph without risk of putting it up on two wheels. If you have a supplies nearby (or at your destination), or if you know you can loot en route to wherever you're going, a utility ATV might work.
inthebutt, stop reminding me that I live in a state with far too many gun laws for a store like the gun emporium to support itself. The closest thing to useful combat gear I could loot would be clothing/tactical gear from a surplus store nearby. Have a gun store nearby, although they don't really stock anything I can't already get except a large supply of ammo. Loads of car dealerships, none of which would be of any use though, unless of course you're apocalyptic automobile of choice is a Mercedes... or a Lexus... or a Toyota... or a Subaru...
"An Air Force A-10 Thunderbolt II flew a show of force and expended flares for emphasis over Salerno after enemy forces attacked a coalition forward base. The arrival of the aircraft prompted an immediate retreat by enemy personnel."