Also, 2 weeks rations is not 28kg in real life, or in any RPG I have ever played. Modern Combat Rations for 1 day weight a little over 1 kg (Australian Army) and that provides 3 meals plus chocloates and coffee. So a reasonable weight you could assume for 2 weeks of 40K Guardsman rations would be 14kg.
Even if they were three meals in one (the description in the Inquisitor's Handbook describes them as a meal) that's still 14kg. Back up to 28kg if you're a Well-Provisioned regiment.
I'm not saying that having to deal with all that weight is a bad thing, it's just a consideration that doesn't really seem that highlighted in the text. If you're in a regiment without vehicles (Drop Troops, Light Infantry, Line Infantry, Siege Infantry), it's a really good idea to consider the weight of all those things you're going to be carrying. This is especially important when you look at the movement rates on Table 1-5 on page 11 of the beta: it assumes you're unencumbered. A warning sidebar might be a good idea.
For bonus reference the total weight of the universal loadout is 13.9kg before weapons, ammo and food. The knife is another 1kg, the flak vest is 5kg, the laspistol is 1.5kg (and its ammo packs weigh .15kg each). 21.7kg before rations. Assuming the conservative estimate of 14kg for two weeks of rations that puts you JUST under the limit of 36kg at 35.7kg. And that's before you get your specialist and regimental standard gear!
I am of the opinion that the matter in which backpack ammo sources is handled currently (and in all previous iterations of 40K RPG) is pants on head retarded and makes no sense. From a Fluff standpoint it doesnt match up, and especialy from a crunch-wise standpoint it's just flat out stupid.
A lot of people gripe about how the backpacks work and I'm one of them. For instance, I've seen a description of the actual tabletop Storm Trooper unit using a Hellgun that says the pack has easily two hundred shots in it. What gives?
Now if you read the beta closely, you can see that the backpack power supply doesn't actually have an ammo capacity listed, so most people assume it's just the clip size of the hotshot lasgun (30). If you trade up for the 25kg standard ammo backpack, you only get 50 more shots for a total of 80 with a las weapon. Now consider that a comparable standard boltgun (1d10+5 X Tearing Pen 5, which would arguably do more damage than the hotshot lasgun anyway) gets two hundred shots out of the standard backpack and you're left scratching your head wondering why las weapons get lumped in with the plasma and melta category. Was it just something they overlooked? The ammo backpack rules really need some looking over.
I'm of the opinion that when they wrote those rules they didn't even consider that the weapon's class (Heavy, Basic, Pistol) might change how much ammo is available from the backpack. Or whether or not you can use it with Launcher weapons (although there is a brief mention in Deathwatch about how one of the missile launchers has a little loader arm that can pull missiles out of an ammo pack). And it does say you can use it with any ranged weapon… so what about bows and slings? Muskets? The possibilities are endless.