SoDak, I like where you are going with the vest idea and have done the same with a TT MAV.
I'm not sure what type of SHTF scenario you are trying to prepare for or where you live. But the Idea of having something that can be worn comfortably and carry whatever you may need to keep going/fighting is a good one.
I live in eathquake and fire country, if there was a massive earthquake, things could turn ugly really fast(NOLA/katrina) and I'd want to have as many mags as I could effectivel carry and still be mobile. For me this is 8-12 +2 on the gun.
-instead of carrying so much water think about a purifying system, I like aquamira as it is light and very effective.
-in place of MRE's think like an ultralight backpacker, freeze dried, dehydrated foods are lightweight and easy to cook. And stoves and pots are getting lighter and lighter. IF you're talking about long term survival think about a .22 and a slew of rounds
-If you're trying to get rescued a signal mirror, flares, and fire starting goods
-IFAK is a must, go with as much first aid gear as you can, that you know how to use

think about the area you live/work in, do you commute? Does it snow? Tornado country? Hurricanes? Earthquakes? Fires? Mudslides? Flashfloods? Or are you preparing for the 2legged SHTF? OR both?
Consider these things and some I'm sure I missed, and plan accordingly. Think about what you really need, and what will keep you alive. If you live in NOLA, I'd ditch everything but the water, and load up on mags.