Asking for a knife for a BOB involves what else might be in it, and what the bags contents are expected to handle.
First things first - gathering water, purifying it, and holding it. Backup rations, too. First aid. When it works down the list of priorities to a knife, then a good 4" folder is first, and if wood craft is possible, a hatchet, if only because an axe is often bigger than the bag, and a bit obvious if the bag is carried into work. (Some do. )
I've had a Camp Tramp, still have a Campanion. The Tramp with a decent kydex sheath was a lot more useful than the Campanion, lighter, which meant I would carry it, and cut better. Thick stock is not always an advantage, any more than a larger caliber is always better.
It also goes to why I sold the Randall #14. Too big and unwieldy. If you need to chop and dismember wood, an inexpensive Fiskars axe will do a better job than a $150 knife, and do it without dulling the knife you might prefer to prepare food with.
If the purpose of the BOB is be as compact and simple as possible, then a lot of knives in the 4" range would do. No BOB will ever be complete for any circumstance or handle every task. There is one kind of BOB that should be avoided, tho, and that is the perfect one with all the coolest gear. It doesn't exist, and those that seek it as a grail discover it consumes cubic dollars in an attempt to create it.
However, we don't mind buying up the discards. It keeps the sale forums going.
