I've seen voystroyans converted into ash waste nomads,
and you can have ork gangs/war bands
squat mining /prospecting/scavenging gangs
Stealer cult gangs
Nurgle cultists as scavvies
Em4/moonraker miniatures carry the old future savages miniatures
It depends on your own interpretation
I quite fancy doing rat skins with fur clad barbarians with guns
And the frostgrave soldiers with bolt action arms that we're on the Post apoc board could be hive scum or caravan merchant guards .