Army Field Manual 21-76 (Survival, Evasion, amd Recovery)

[Thudz]

Some of the essentials in my BOB :

Fire

Starter - http://www.cheaperthandirt.com/CAMP223-1.html

Water :

Filter - http://www.cheaperthandirt.com/CAMP156-1.html

Air :

Respirators - http://www.cheaperthandirt.com/MASK8511-1.html

Shelter :

Wool Blanket - http://www.cheaperthandirt.com/CAMP219-1.html
Waterproof Tarp
Mosquito Net - http://www.cheaperthandirt.com/CAMP250-1.html

Clothing :
Socks
Underwear
Waterproof Poncho

Food :
Ramen x 4
Snickers Marathon Bars x 8

Tools :

Machete - http://www.cheaperthandirt.com/59284-1.html
Multi-Tool (Leatherman)
Rope - 3/8" x 75' (Not For Climbing)
Flashlight (600 Lumen LED)

Misc :
First Aid Kit
Hand Sanitizer
Multi Vitamins
Local Map with Topology (Upgrading soon to Garmin Handheld GPS)
Duct Tape

I have lots of other odds and ends but this is where I'd start if building a bag from scratch.