Troops for the imperial army
Available disposable manpower is the resource. Each world has a certain number of battalion sized units proportional to its population. There are tables for this in the JTAS. Some units stay home, aka the army to defend the planet. Garrison duty, internal security, law enforcement, disaster relief, national guard, protection versus incursions vargr, sword world, zhodani, aslan, what have you. Some manpower and cash/taxes are siphoned off to support larger, more sophisticated, more expensive imperial units. Everyone must offer the emperor their required levy. These citizens are shipped off and trained, indoctrinated and serve in imperial army units. They are equipped at imperial standards. Book 1 draft and enlistment odds are predictive on the relative abundance of who gets in and how long they stay. With dice rolls you get a lot of 22 year old army captains (mint green company commanders) skilled in things like rifle, smg, tactics, ATV and air raft. Basically cheap mechanized infantry. They are forward observers and occasionally medics. Artillery and heavy weapons really had to wait for Mercenary. Not many with Vacc Suit 2 for battledress. So our combat rifleman doesn't appear to have TAC missiles nor FGMP-15s either. I hear the imperial marines snickering in the background, but they are clutching cutlasses and revolvers, so they can shut the F up. Book 1, LBB has definite impact on the disposition and composition of "imperial" forces. Of course, as always your mileage may vary.