>>29859508
Why not just have them with SM scout biker mines? Make any piece of terrain dangerous.
>inb4 people buy a bunch of cheap squads just to mine everything on the enemy's side of the table
As for cultist weapons, I guess they could throw in at least a grenade launcher and krak grenades, if nothing else. Flamer, stubber and grenade launcher seem like simple weapons you'd find. Nothing fancy, but something you could whip together in some shop or steal from officials (local enforcer tear gas launcher, etc.) Give the champion more varied upgrades, like bolt pistol/bolter, plasma pistol, power weapon and melta-bombs. But I'm guessing we'll see this in the next codex, once they get better models for them.
You could also make a storm trooper equivalent "dark pact" troopers, which are like elite cultists, troops that have truly gone down the dark road and gained some respect from their masters. Smaller squads with heavier armour, maybe bolters/bolt pistols for weapons and 2-3 special weapons to boot, inc. CC ones. You could easily use regular cultist bodies with additional torsos, heads and guns.