One fine day I was generating a Storm Trooper as part of a Drop Troops Regiment when it hit me. I couldn't carry my standard loadout on the move without becoming fatigued after three hours of marching.
Given that the average Strength and Toughness bonuses for a character in Only War hover around the 3 range, you're looking at a maximum carrying capacity of 36kg in the beginning of a campaign. The problem is especially bad for anyone part of a Drop Troops Regiment (the grav-chute alone weighs 15kg), but also rapidly becomes a problem for Storm Troopers, as their specialist equipment weighs 31kg by itself (15kg Carapace, 16kg Hellgun plus backpack). Then you factor in the universal Guardsman loadout and you're way over the limit.
(For reference, from pg. 182 of the Inquisitor's Handbook, as these weights are missing from the Only War tables: the rucksack weighs 2kg, hostile weather gear weighs 2kg, the Primer weighs 0.3kg, the lamp pack weighs 1kg, the grooming kit weighs 0.1kg, the mess kit weighs 0.5 kg, the tool kit weighs 1kg, the blanket and sleep bag weigh 4kg, the entrenching tool weighs 2kg, the uniform weighs 3kg, and a pack of four sandbags or so weighs 5kg.)
Combat rations weigh 1kg each , so assuming you eat only once or twice a day that's 28kg in food alone, per guardsman, for your standard ration allotment.
I sure hope your regiment is mechanized!