I am working on my GB/BOB as well as building out go bags for the family. Mine is a 50L, wife is 40L, son (<10 yrs) is 35L and my daughter (<5 yrs) is a 8L shoulder pack. I also have another 8L that I keep in the truck as a get home bag.
I broke my bag setups down into the following:
Water - My bag has a lifestraw and tablets. All bags have collapsible water bottles. I carry means to boil water as well.
Food - Millenium bars currently, will add other as I go along
Clothing/Shelter - socks/underwear/etc, emergency blankets (multiples in each pack), ponchos. I carry multiple means to start fire in mine and wife's (including homemade firestarter balls, matches, lighter, ferro rods).
First Aid - Basic first aid. Have a triple A bag in the 8L get home. In my BOB I carry basic First Aid, SAM splint, etc.
Sharps/Lights - Flashlights, headlamps in all bags. I carry at least 1 fixed blade and a folder in mine. Folder in GHB, wife's bag, will prob add to son's in near future.