My BOB is fairly simple. I try not to complicate things anymore than I have to so I pick most of my gear according to how well it will help me sustain myself. For instance, I keep a machete, hatchet and knife close at all times since they can help me make shelter, procure wood for fire, and set traps for food. water isn't a very big issue around here since where I live it's hard to walk for five minutes without running into a creek, river or lake, all of which are surrounded by springs that are naturally filtered by the limestone bedrock which is promanent here. People actually drive around with jugs to collect spring water because it tastes better than city water.
With water comes fish and they are easy enough to catch with simple line and hook. Bait is as simple as looking undeer rocks for bugs. If the line breaks or I lose a hook, I carry extras, but I can always find more hanging from tree limbs or snagged around rocks on the bank. Growing up, this is how I supplied my tacklebox. Snakes and turtles are pretty plentiful and make a decent meal in a pinch, so food isn't really that hard to come by.
My BOB mostly has sharp stuff for cutting or chopping, first aid kit (which I have been dipping into recently due to a prolonged illness), some fire making gear (lighters, magnesium block, magnifying glass, etc.), a few tools that I don't know if I will ever use but might come in handy (a chisel, pliers, philips head screwdriver, and ratchet style PVC cutter), some skewers for cooking or spearing, and a few food items that I particularly enjoy cooking over the campfire.
I try to keep things that I can use for more than one thing if I can, and most of it is merely for helping me get set up to produce my own tools, food and other things that I might need. My everyday carry items are pretty much a couple of pocket knives, a swiss tech microtool with led flashlight keychain, and usually a couple of small shovels that I use when metal detecting. Other than that I don't carry alot of stuff around with me.