For all of you getting started in building a Bug out bag, sportsmansguide.com has a used marine corps assault pack which I'd say is perfect. Look up part number D3N-281748. It's only $30 and it's a 1520 cubic inch capacity bag, and should fit you fine as a bugout bag.
Your bug out bag should be something that your GHB can attach to if possible, and do NOT duplicate items unless they're stackable.
Bug out bag rules:
1. Keep it light enough to carry without exerting yourself (hike 3-4 times a week with a double weight pack, at as much distance as your time allows)
2. Your Bag is ***YOUR*** supplies, each member of your party must have their own.
(Exception is for small children, obviously, spouses are NOT exempt, and neither are kids old enough to carry a backpack)
3. A bug out bag is meant to be 72 hours of survival supplies. Not 3 weeks, not 24 hours, 3 days. That's it. If you can't make it to a hole up location where your longer term supplies are located within 72 hours, you're screwed. It's really that simple. If you want a longer term survival bag, build that, it's not a bug out, and has a totally different load out in mind.
4. Pack your bag based on expected climate and terrain. If you live in the mountains, pack a mountain survival bag, if you live in an arid/desert environment, pack differently.
5. Before you pack, PLAN. You should have 3-4 plans of action based upon different scenarios, and each one should have multiple contingencies. If 100% of your escape plans revolve around you having your xterra, 100% of your contingencies had better revolve around "oh crap my xterra's gone". Your "backup location" should be something you can realistically make within 3 days **ON FOOT**, preferably no more than 2 days hike.
6. Once you've established your plan of attack for movement/evasion and escape to a backup location, pack appropriately.
Remember, you're packing for your survival, don't go for luxury, go for small and light, especially for your tent/shelters. As Mac and Deeb can attest, I have a **massive** tent for everyday camping, my evac bag (note, not bugout bag, I have a larger evac bag) is getting a small 2 man "burrito" style tent, if you have room for this type of stuff in your bugout, you're doing great.
General ideas:
550 paracord: get it in a color complimentary to your terrain, and don't get off brand stuff, you want the quality kind. At least 100' of it, a 100' length of paracord should take little to no space, so, don't sweat it, better to have too much than not enough.
Knife: fixed blade, sharp, preferably not some gimmicky "survival knife". Remember, your life may depend on this, get a decent knife (as a rule, if you didn't spend at least $100 here, or if it has the name or logo of a TV star idiot "survivalist", you probably need a better knife)
Fire starter: one or more fire starter kits, preferably with some good dryer lint for tinder.
Hatchet: use if needed to gather small firewood, make it sharp, and the type that's thick and heavy (note: the smittybilt trail axe does NOT fit this role)
Sleeping bag/blanket/whatever: this is for on the run, I suggest an army style wool blanket. It'll dry easily, keep you warm even if wet, and, most importantly, it's small.
Clothing: 2-3 changes of clothing at most. If you're a BDU's type, make one of those changes of clothing a regular t-shirt and jeans. 4-5 pairs of socks are good too.
One extra pair of boots wouldn't hurt either.
Firearms: here's where I'm the odd one, do NOT put a gun in your BOB. You'll have your pistol in your GHB, and your rifle and ammo should be at your fall back location.
If you're walking through the streets with openly displayed guns, you won't get away, and if you're tearing a gun down (other than maybe a Henry AR-7 survival .22) you're wasting space.
Otherwise, you know your terrain.
Get the army survival manual, first aid manual, and SERE manual and read them, commit them to memory, and practice them. They'll serve you well.