It would be nice if we could all hit our perfect BOB the first time out but I haven't known anyone who has actually used theirs that has.  It seems to be more of an on going project that you improve with time.

An approach I like is go cheap on the first one, real cheap.  Then as you learn what fits your needs, upgrade.  You can then convert the first one to a GHB.  Otherwise you end up like me  and a lot of these other guys with an almost surplus store of gear.

In planning, I think its best to define your need.  There's all kinds of BOBs.  

Here's a write up I did on BOB types.

BOBs

Anything as important as your survival shouldn't be what best suits us but suits your needs.  You see everyone’s need will be different and everyone’s perception of what is important to a BOB is different.

Keeping in mind, "Prepare for the most likely scenario first and least likely last.” And “the key to survival is adaptability.” one should define what your BOB needs to be in order cover what suits your needs.  

Planning or consideration of the most likely needs is the first step to BOB planning.  I refer to this as Bugout Philosophy.  This includes how far is your worse case you plan to go and under what conditions.  No bugout plan should be without a destination.  Once you determine your worse case scenario, then you will know how long the BOB should sustain you and what terrain you may be faced with.  Most people prefer to Bugout by vehicle, BOV, and BOB as a backup plan.  

There are two basic schools of thought on BOB packs, tactical and non-tactical.  I often think of this as “Don’t mess with me” or “ I want to blend in and not draw too much attention”.   Of course, this is very geographic.  Some places in this country a man dressed in camo with military gear will barely raise an eyebrow, while other places it could draw a lot of unwanted attention.  Depending on the scenario, you may want that attention, however usually open carry armed regardless of what you wear says a lot.  

There are a number of different types of BOB concepts.

BOV/BOB
This is a BOB kept in a vehicle usually with the versatility to add or subtract gear from the BOB or BOV gear.  

GHB
This is typically a smaller pack kept in vehicles or during travel to provide supplies to make it home in an emergency.  

Short-term BOB
This is usually a moderate size BOB fitted to give you the gear necessary to sustain life for up to 3 days.

Long-term Bob
This is usually a large size BOB designed for long hauls with typically a 3 days of supplies but with the capability to gather more food and water.  

GEAR

Like most things gear is customized to the possible scenarios for a given geographic area as well as personal needs.  This varies a lot but there are some common gear items that are more essential than most and they center around the basic needs for survival which is water, food, shelter, etc.  A very good approach to gear planning is try your best to keep the weight to a minimum however having backups for each essential piece of gear.  A recent study showed most long range hikers keep their gear weight to around or under 40lbs.  

Here’s a short list of common items:

Water and carry system
Options vary here from commercial water bottles, canteens, Naglene bottles, and hydration bladders.  Long-term BOBs usually have a filter system and water treatment system.

Food
This is very much a personal preference as it is in life.  Some of the most popular are freeze dried foods since they are light, easy to prepare, and store well in various temperatures.  Fast grab food items such as jerky, or food bars are also very popular.  MREs with heaters are also popular for those rainy days where a fire or stove cooking is not necessarily a good option.

Fire
Since man became aware of fire it has served as a survival tool.  This too is very personal selection ranging from Zippos, butane disposables, high tech lighters, matches, and flint/steel methods.

Compass
Once again this is scenario, geography and personal preference.  Most emergencies however being able to tell basic direction is essential.  Maps of your potential areas are also important or a good understanding of the area you will be traveling.  Topographical maps in addition to road maps are very common.  If you are using your pack, the odds are very high that you are on foot and the ability to go off road has many advantages.  A GPS is an invaluable tool but it isn’t a replacement for a compass.  They simply don’t works sometimes due to geography and batteries have finite life.  

Shelter
A need for a shelter varies by geography and scenarios but is a typical piece of gear even if it is simply coat, poncho, or small pack tent.  Geography plays the biggest role in this selection since what works in the desert can kill you in an artic climate and vice versa.  In spending the night, being able to stay dry and warm can be a life saver and at the very least a good nights sleep will allow you to maintain your energy level better the next day.

Sleeping Gear
Geographic and season dependent, the options here are space blanket, blanket, poncho liner, ultra light bag, and sleeping bag.  

Flashlight
Personal preference item, it can’t be stressed how important being able to see at night is.  Preferences vary here as how many products on the market will testify to.  The most recent trends are ultra small lights and head lamps that keep your hands free.  LED technology is very popular due to the long bulb life and low battery drain.  Other popular options are tactical lights which are high output and use long lasting lithium batteries. Spare batteries are a standard item for flashlight carry.  

Knives
Another very personal preference, it is still an essential part of any gear list.  Usual types are fixed blade, folding blade, and multi-tools.

Defensive Weapon
This will vary by scenario but by far the most danger to anyone on foot is man and a handgun is by far the weapon of choice due to conceal ability and speed of deployment.  This is followed closely by preferences for hunting or the combination of both hunting and defense type weapons.  Tactical is probably the last option such as military field layout but by no means not popular.  

First Aid Kit
This is a typical found in almost all BOBs and BOB types.  They vary in size and type but the basic needs is to handle cuts, blisters, insect bites, prevent insect bites (DEET), disinfectants, and pain meds.  Required prescription meds should be a major part of any BOB planning.  The usual preference is a kit system, however few people don’t ever use them without adding to the list of items.  

Line
This is personal preference as well but the uses for line are so numerous it is typically considered essential gear.  A favorite is paracord 550 which is a strong line 550lb rated, light, and the seven strands can be stripped to be used for numerous items.  

Spare Clothes
Top of this list is socks for if your feet stop you stop.  Everything else is season or geographic specific.  The assumption here is that a survivalist will always dress for the weather and pack clothes should be replacement.

Lot of basic information here and I hope it helps in your planning.

A lightweight shot-term decent BOB with basic gear can be as inexpensive as under $100 not including defensive gear of course.  A good long-term can cost as much as a gun.  Short-term being defined as less than three days and long-term greater than three days to weeks.  

I have probably less than $100 in all three of my GHBs, I keep in my cars but probably have about $600 not including guns or knife preference in my long-term BOB but probably cost me half as much more to fine tune it to what I found I needed.  The biggest mistake was buying crap I thought I needed but after getting some field time finding out it either added to much weight or wasn't needed.

Humping this stuff and using it is the fastest way to get it right.  Otherwise, you can buy the best of the best in gear to only find you don't need it.  Its one of the reasons I recommend go cheap first.  Its harder to prune something you paid a bunch of money for.

Tj