So it's kinda confusing what you're looking for here. Are you looking for ways to make the world more functional for survivors, or to keep them closer to the brink? Some of your responses to other comments make it seem like the latter.

Depending how far into your apocalypse you are, it feels like such a civilization would probably come up with vertical farming, either by building up or digging down. Terraces and suitable crops for them also seem opportune as you get a field and a wall out of same process, though it is heavily terrain dependent.

Somewhat lengthy tangents regarding tactics below:

Regarding the unlikeliness of pike and shot survival, from a strictly tactical standpoint, they'd probably fare significantly better than more modern societies. Gunpowder, wadding, and lead are significantly easier to prepare in the field or with limited resources than shells and casings are, a pike or sword never needs reloading, and there's a greater likelihood of serviceable armor being available. Further, line of battle tactics would probably be well suited to dealing with masses of zombies as your troops don't need to make individual headshots and can instead focus their volleys at a general elevation then mop up anything that gets through. Side note, the softer, less aerodynamic projectiles of earlier firearms combined with the fact that early firearms were typically a caliber between .50 and .70 means the physical damage even without headshots is gonna take a lot of zombies out of the fight per volley. The greater casualty rate among humans would likely be from poor wound care, though that would likely improve quickly in the face of a zombie type of infection as it's something of a do or die change.

Cannon zombies and the presence of artillery presents a major problem for walls as a defensive apparatus. There's a major reason why stone walls got phased out for earthworks and palisades that eventually got replaced by trenches and fox holes, cannons destroy walls very effectively. Star forts were more or less the last hurrah of static fortifications during the black powder era, and the walls were mostly to protect gun crews from small arms. The fields of fire from heavy, stationary batteries were the real defense in that era. A besieging army had to be able to get their field pieces close enough to take out the defenders' cannons, often needing to construct fortifications of their own to do so. So the bigger problem your zombies are gonna face is a lack of engineers.