A BOB is a backpack or such that you can grab from your house and carry with you when you need to get out of the area as fast as possible. Be it in a car, walking, on a bike, ect.

A truck bag is one left in the vehicle that has survival stuff, but has a lot of vehicle specific stuff and is usually left in the vehicle.

A 72-hour bag, can be considered a BOB (the terms are used interchangably), but is sometimes considered the opposite, for when you need to stay in your house or in the area. Probibly for when it is unsafe to bug out. Usually this has more in the way of food and water, so it is too heavy to grab and go.

That is my understanding, I may be totally off. <img src="/images/graemlins/smirk.gif" alt="" />