Armoured vehicles like tanks and APC's are a rookie mistake. An M-1 Abrams has a jet turbine engine that is a bitch to maintain and takes a crew of 4 to drive. You can get away with having a driver and a TC but that'd be rough trying to get around in a urban enviorment. A
Bradley or an M-133 is also a tough one to go with. If you break track you'll be assed out and not to mention that these beasts drink fuel by the gallon.
The best way to go is a nice crew cab pick up. Something with a low profile that you can drive through the doors of a Costco and take all of Britt's stuff and still seat 4-5 people (I'd stick with at least 4 people when doing anything). Weld some chainlink fence on the windsheild and rear window and rebar over the door windows and you're good to go. If you're worried about other survivors shooting at you get some 1 inch steel plates for the doors and around the engine block that you can easily replace and viola' perfect zombie vehicle.
CrowBar I'm resisting posting a picture of a Nissan
Frontier LOL!