It depends on several factors, where you live or are determines climate and the types of clothing, need and means of heat, shelter, food, etc. I'm in a very rural area, I mean the boonies for over 100 to 150 square miles. I use an older Kelty back pack thats olive drab, and I have camo'ed the frame. I keep 2 good quality compasses, map grids, and have 5 or 6 topo maps that cover the area around me in a homemade map tube made from thin wall pvc pipe with threaded cap that attaches to the pack. I carry a carbide fire starter, small containers of sawdust/petroleum jelly mixture, and a zip-lock bag of dryer lint, waterproof matches, several bic lighters as my fire starting goods. I carry a supply of fuel bars from the mil-surplus store and a small folding stove, and a set of nesting pans that are about 6" in circumference and tall, a mil mess kit, canteen cup, and a knife, fork, spoon, opener folder. A hatchet/hammer/prybar combo tool, folding mil shovel, a 15" bowie, an 8" fixed blade, a skinner/gut hook, 2 lock blade folders, and a Leatherman multi-tool. All my clothing, coats, bibs, etc. depending on the season is in a mossy oak camo pattern. The military digital patterns are only effective if you are hiding in a gravel road or your grandma's couch, and actually stand out in the woods. I carry a mini mag light with colored lenses, and several other micro lights as well as a multi-bulb and red led head lamp, all that use the same battery and extra batteries. I carry a Marlin Papoose take-down .22 rifle and a supply of ammo for taking small game to eat, a .45acp semi-auto, 3 mags, and a supply of ammo, and my customized AK-47, 6 mags, and ammo for defense and taking medium game like deer. I have a camo one man bivvy tent, a small camo tarp, and have sewn 2 5x10 camo burlap sheets into a 10x20 camo sheet for making an undetectable hide, or as a sleep pad for my military extreme weather mummy bag. I keep a roll of para-cord, 4 lightweight military tent poles, and a bag with 10 to 15 metal stakes made from those metal rods that convenience stores hang chips and candy from. I have put grommets around the perimeter of the burlap cover so I can configure it many ways in making my hide. For water I carry military canteens, 2 one quarts with covers, 2 two quarts with covers, a bottle of water purification tabs in each ones pocket, and a 1.5 liter water resevoir with drinking tube.
This is the basics I carry, or keep ready to carry should the shtf. I have other survival gear in my pack, but that's the personal preference items. There are several web sites that offer good BOB and survival equipment/gear lists. The best thing to have about you in a shtf situation doesn't go in the bag, it's your wits. There are some groups around the country that do shtf drills, and being basically alone in my situation, I do practice runs too. I grab my pack and gear and head into the woods nearby my house and stay for 3 to 5 days. This will tell you what you really need with you, and the items you could do without, practice making your hides(hides are your "camp" site that are camo'ed and blended into the surrounding land by camoing your bivvy, using natural foilage the blend in better, and have a place to rest, etc. being unseen), shooting and cooking wild critters, gathering other wild/natural foods, and will make a person more prepared and skilled when the feces hits the fan. Just my ideas and thoughts, and hope I gave you place to begin on preparing your BOB.
"Designated Marksman"-The guy who hunts down the enemy and shoots him in the head.