Anyone who has seen my minis knows I like to upgrade them in all kinds of ways. One resource I have found quite helpful for creating my Imperial Guard forces how I want them has been the Assault Group. This company offers white metal equipment from historical ranges, which non-the-less are highly useful for kitting out your assault teams, whether they are Pulp, Historical, Grimdark or all the above.
I will not include common pieces of equipment that you presumably have tons of (such as bolt action standard rifles).
I will not go into Medieval melee weapons that could be useful here. There is a ton of them. Although there are some that are definitely at home in the hands of Soldiers, Cultists and gangers in the universe of Warhammer
40K... or plenty other universes to be honest!
So We will Start Chronologically
WW2 British
WW2 German
WW2 Japanese
WW2 Soviets
WW2 USA
Vietnam War Commonwealth
Vietnam War Viet Cong/North Vietnamese Army
Vietnam War USA
Modern British
Modern Russia
Modern USA
And lastly:
Diorama sets Which offer potential for scatter terrain or some flavour for narrative objectives.