Biggest issue with creating a BOB is keeping it fresh, most people make one up, then never touch it for years, when they do they find they have loaded it with lots of 'perishables' like dry cell batteries, medicines, food, etc that has gone either badly out of date, or just plain bad. My biggest example is a flashlight loaded with Duracell batteries, in a couple years the batteries will have leaked so badly that you might not even be able to remove them, ask me how I know!!!
IMHO, Creating a BOB is different than a survival kit, generally if you are bugging out you need to capture and take items that will enable you to survive, CASH, passwords, credentials, account info, etc. will enable you to be resourceful. where survival WILL require more food, water, clothes, light and power, but not necessarily to depart the locale.
Think hard about what you're trying to protect against (survival in place vs. need to relocate), maybe even a combination of kits. Also, think about your locale, in lowland or coastal some type of flotation equipment may be beneficial or necessary, but is it necessary in the high country?