Well, when everything is loaded and filled, I'm humping 12 pounds of water and I'm not in the desert, so my idea of normal might be a little different....

I would normally say 1/6th your body mass if you aren't in used to it but have a good back and are in good shape. But remember, it is your back, your bug out plan and your BOB, so the biggest question is, can you carry it reasonably comfortably for 10-16 hours a day, for as long as it takes to get where you planning on being if your car doesn't make it.