Modular transport, the same kind of 'modular' we see with the power armour(s), has a similar #x# grid layout, with which you could put
Speed Increasing units, Cargo Modules to allow carrying space, Volatile Shields (small amount of damage-over-time in an area around the specified transport), Armour plating increasing hitpoints/resistances, Offensive Systems (lasers, gun turrets, discharge mines that sort of thing) - with regards to being able to shoot out of your car interestingly enough

Let me know what you guys think!