Interesting question, but rather general. How far do I have to walk, how much water is available, what season?

My SAR pack, available 24/7, in all seasons, could support me for at least 72 hours. One of my compatriots put it on a scale and it weighed 41 pounds, with about two liters of water. I always tweaked the contents depending on the season - in the summer in the desert, it essentially became a giant water bottle. The winter pack was actually lighter. In a true BOB, as opposed to a SAR pack, I would not include as much first aid gear nor as much climbing gear, but the contents would weigh about the same.

Now I am a bit older, and I would try to lighten my pack to somewhere in the 30-35 pound range, a goal that is feasible with some of the newer fabrics and gear that is available. I can easily handle that load indefinitely, and heavier weights for short periods.

The key question is the amount of water you must carry. Nothing else comes close in terms of weight.