US Marauder Companies

[Legbreaker]

If they weren't organised until post nuke, then I'd imagine the requirement for airborne/parachute/halo qualification would be dropped.
Emphasis would be placed on physical fitness, long distance marching, horse riding, and vehicle skills, in addition to rifle, machinegun, demolitions, boobytraps and mine warfare.
I see their role being similar to that of the Finnish Sissi units - stay behind the lines acting as guerrillas and saboteurs, living off the land and whatever they capture from the enemy.