First off, scale down - thats a heavy bag. Ditch the following:

• Tyvek suit: Don't need it, if you're in a situation where that's required then the world is an atomic wasteland or overrun by zombies. Remeber you're making a 72 HOUR bag. Not a TOTAL COLLAPSE OF SOCIETY bag.
• Swap out the p100 for some disposable masks, or remove it entirely
• Spices....if you really want them then okay. But this is really a comfort thing, and a little bit of weight you can chip off. Remember his is a 72 hour bag, you don't need your food to be gourmet.
• Boresnake. You can use your bandana and a stick. Plus, how much shooting do you plan on doing in 72 hours? Keep your weapons cleaned and oiled anyway and it wojn't be an issue.
• Knife sharpener. Same thing, you won't be cutting so much in a 72 hour period that you'll need to resharpen your knife.
• wire saw. These things always suck. Always. Add a good tomahawk instead.

ADD the following:

• A shemagh you can find them MUCH cheaper than that, but there's an example. Shemaghs are, imo, better than a bandana (I have both in my BOB)
• Sodium/Electrolyte tablets. I live in AZ, the desert, cold weather is not an issue for me. Potentially walking in extremely hot temperatures is, however. So I like to have a supplement that can keep my salt up when I'm sweating my ass off.
• Pup tent. Ditch all your sleeping gear, too heavy, don't need it, you can sleep on the ground and be okay for 3 days. This tent is small, durable, LIGHT, and bright so it can double as a signal panel.
• A mirror. For signalling.
• A tablet and pens / marker. You need to be able to record information.
• Canteen cup, and / or some stainless steel water bottles. For cooking, and you can boil water in them if you need to.
• A magnifying glass. You should have 5 ways to start a fire. Use that sun. Find a small one, like a jeweler's
• Sawyer Extractor. For snakes and bugs. Don't know if snakes are really an issue for you, but for me, in AZ, they are. The Sawyer extractor is excellent and requires no cutting of the bite area like some snake bite kits do.
• Maps of your area
• Chem lights
• Road flares
• A crank radio. Because you need to be able to gather information and keep up to date. Knowing is half the battle. I HIGHLY recommend that one I linked, It works great.
• Another knife
• Tomahawk I am partial to that one, because it's sturdy as fuck and can double as a hammer.

Your med kit. Don't ever buy a med kit, build one. I was an army combat medic for 8 years so my medkit is very different and very specialized, but generally speaking any premade kit suuuucks.

The way I think about my BOB is like this: I live in AZ and I travel a lot, so I through it in my trunk when I do, if I'm stuck in the desert for three days, what will keep me alive?