another angle....maybe some of you've heard this one before...but it goes along with the belief/possiblity that the BOB might end up being something you live with and/or out of for a very long time....its the two bandana approach, one used for TP. You have to admit it will last a long time compared to one roll of TP!
My attitude toward my BOB is what if it becomes my only source for even a year? So things like soap will have to come from nature (Beech leaves, soap plants, etc.).
Of course the more you know the less you have to carry...e.g. Bushcraft and the study thereof....this approach leads the BOB as providing methods of obtaining food post the 3 day supply inside,,,,,why not learn how to build 50 different traps? many are simple variants of the other.