You pre position caches along your likely routes of movement and likely routes of movement.

ok...25 years ago, I sailed through O'Hare, agiley leaping obsticles while hauling 2 large suitcases and a large purse (aka-small suitcase), resembling OJ Simpson all in high heels and a skirt business suit. 10 years ago, I trudged (f#$@ agile leaping) through Heathrow, lethargically dragging one large suitcase, with barely enough air in my lungs to holler at my obscenely long legged companions to slow their arses down.
I figure that now....I'm staying home.

Turn it into a "vehicle BOB", and as others have said RE-INVENT it! If your BOB is intended to sustain you for 3 days to get you out of harms way or back home then that is all you need. I think that many folks BOB's are actually refugee bags... I am not big on weapons or large amounts of ammo in my BOB as I don't need to engage in a 3 day war on my way back home. If you find yourself involved in firefights, then you are already in a big mess!

Just carry the basics to get you where you need to go.

If you have a BOB that is too heavy to tote, and need it for more than 3 days, you need to reconsider your transportation methods. Add a bicycle with some ability to carry your load on it or <insert other travel mode here> Even if you can't climb hills with it fully loaded... it is better than humping it.

Just my .02

You should 1) start hiking with the pack, loaded with a weight to say, 50 LBS, and work your way up to OVER what you'll normally carry. This way it trains you to be able to carry the weight.
2) Take the FULL kit out and try a weekend with JUST the contents of the bag. See how they work for you, and what you end up NOT using. Review with you and the wife how it went, what you wished you'd have had and what you didn't really need, and adjust from there.
3) Figure out where you plan to go to, and cashe food, ammo, and other supplies you may need along the way. You'll run out of food eventually, it's better to be able to go to a spot and get more, and salavage, then to rely on salvaging alone.
4) And this is a personal thing for me, I plan to not only have a GOOD bag, but set up my vehicles for us to make a new start someplace else. The idea is for my vehicle to get me as far as I need to go, and, if I need to be on foot from there, I'll have the GOOD bag to go the rest of the way. I, myself, am just starting in this however, and being po' folk, don't quite have everything together yet LOL. AND, still working out planning, although the main one I have isn't bad.

A backpack should be prepared carefully, You are only going to be able to live at most 2 weeks from a back pack. Every item contained should be carefully considered.
And think of this, what is the "intent" of your reason for the load contained.
Knowledge and training will extend the time you will be able to endure, and lighten your load.
Why do you think the Military has to be resupplied, and logistics is so important.