I have several BOBs. I prefer duffel bags with several side pockets . Something like this one but different colors.
Why a duffel and not a backpack?
Well. I have not had an emergency so far that I had to carry the BOB for a long distance, so out of practicality I thought a duffel bag is better for me. One is in the car trunk . One is in the house.
I also beleive in the "cache" concept, but not including any digging or burrying. One BOB is pre-positioned in my fathers house. Another one is pre-positioned somewhere else. So if I lose my BOB, I think I can reach another one.
Just an idea.
Some folks are addicted to buying "stuff" , so when a knife or flashlight is not your "favourite" anymore and you feel the urge to buy another, the one you are "done with" can very well be used for a cache. Collect you less desireable items in a BOB/cache and store it in your brother/sister house in a different state. You never know when you might need something.