Your BOBs should have a separate individual "Personal survival kit" with things like a fire starter, a knife, bandana, must-have-medications, and other small bits that are focused on your AREA, SEASON, and anticipated ACTIVITY. These should fit in a fanny pack or similar mode of carry that WONT get left behind EVER. This is slightly different than a BOB, but should be part of it, IMO.
In the actual BOB, have at least one double for EVERYTHING in your personal survival kit. This bag should have other, more long-term and general use types of items. Everything from a collapsible cup(That can be used for boiling water etc) to even other containers, a hatchet, a gun & ammo, para cord, a tent, etc.
The age and physical fitness of those carrying the bags should be considered also. The weight or contents(Like weapons or knives) might be reviewed depending on who is carrying what bag. Get a couple or few good survival books, and keep them in a water prrof container(Like a plastic bag) in the BOB that can be referred to along the way. Even if everyone in the party has read multiple books on it, it's good to be able to refer back to things that were forgotten.