Just make items in backpacks lower your maximum fatigue like equipped weapons.
Then taking four billhooks or greatswords isn’t that attractive any more.
Unless I am wrong and they lower max fatigue already.
Also adding visible slots with items inside backpacks so people know what soldier carry and for fast switch without switching view to inventory will be great.
Like that:
BTW Any chance for consumables?
Like bottle of vodka to boost morale(with some penalty) or bandages to stop bleeding?