Most guys I know who do similar extent of hunt without the vehicle all clued onto back country meals a while ago, finding the ones that you don't mind eating is trial an error but its easy to have 10+ days of food in a reasonably small package, which is heaps.
I get what ya wanting to do though and its the great white hunters dream to do so, but the 308 will cleanly take a rabbits head off an theres good abundance of game in most regions of Australia that you would be able to hunt down a young animal and take what meat you need, if you feel the lack of meat is a problem.. in the bush trophy stags can also be eatin, not uncommon an if needed a backstrap is as good as anything..
for 3-4 days or so I can carry around 22kg comfy and up to but not much more than 25kg , this includes a 7mm08 (2.7kg) a tent an sleeping, plus Water - water is heavy but if you're confident you can find it up there / out there , then it can aid in more room for back country style meals or a few extra nibblies.
horses for courses though everyones criteria varies, some are not wrong nor are others right... the whole backpack game is to be tailored to your needs and not someone elses opinionated needs.
to be frank , two guns is silly unless the other is of ultra light weight and the main rifle is in 'ultralight' class.
Two loads for one gun is the lightest option to it, Canadian I know will load 'squib' loads for popping grouse out of trees or squirrels with a 338 winmag , which sounds like that's what you want to do