Worst case scenario, you can use run-flats, but they're not ideal for off-roading. What you really want is a proper set of airless tires, like the Michelin Tweel shown here. They're cutting-edge tech that uses no air pressure whatsoever, so you're not going to get a flat at a really inconvenient time.
Invest in some quality bulletproof glass
Zombies aren't going to shoot at you, because that would be silly, right? But when you’re plowing through a particularly aggressive throng and rotting body parts are flying all over the place, you'll take comfort knowing that nothing can bust through your windows.