I use to have a BOB, but decided...where in the heck am I going to go? Its best to shelter in place unless it is more dangerous to do so than becoming a refugee.
Survival gear is only as good as the person carrying it. You need to have a solid skill set, mind set, and physical conditioning. The more time you spend outdoors the less crap you need to carry.
A comprehensive 3-day kit for a relatively fit (physically and mentally) person who has some experience (hiking, camping, firemarking, snaring setting, water purifying, fishing, etc etc) is:
Shelter: USGI Poncho, GoreTex Bivy, Sleeping Bag, 550 Cordage, Ground Cover (can be as light as a space blanket - remember one layer below is better than two above)
Water: USGI Stainless Canteen Cup, Katadyn Filter (Hiker or Pocket), Bandana (to strain debris), (2) 32oz Nalgene
Fire: Bic Lighter, Petrol Tinder Bottle (emergency use only - fill a 35mm film canister with cotton balls soaked in petroljelly), Fire Steel
First Aid: Moleskin, CAT, QuikClot Sponge, H&H Compressed Gauze, Tweezers, Antiseptic, Antibiotic Ointment, Duct Tape, ACE, Adhesive Bandaids
Food: (3) 3600 Calorie Datrex or Equivalent, Salt, Small Fishing Kit (very heavy fishing line works well for snares too), Ruger 10/22 TD (add Tech Sights or a LOW MAGNIFICATION Leupold Scope like a 2-7x33mm VX2) with Ammunition and Cleaning Kit; Spork
Tools: 6-8" Fixed Blade; 3-4" Fixed Blade; Sharpening Stone
Navigation: LED Headlamp with Spare Batteries; Compass & AO Map; Whistle; Chem Light
Outside of "urban" areas with which I would include a HEALTHY compliment of ammunition for my FN SCAR I can't really think of many scenarios where a person couldn't survive in a suburban / rural area for AT LEAST 3 days with the above. Obviously serious injury limits your chances of survival anywhere / anytime. Desert survival is a completely different animal with which I have no experience.
Frankly, I think a person could get by on substantially less if the weather isn't arctic cold and/or constantly wet. A minimalist approach:
Shelter: USGI Poncho, 550 Cordage, Emergency Space Blanket
Water: USGI Stainless Canteen Cup, (1) 32oz Nalgene
Fire: Bic Lighter, Fire Steel
First Aid: CAT, QuikClot Sponge, H&H Compressed Gauze, Tweezers, Antiseptic, Duct Tape
Food: (1) 3600 Calorie Datrex or Equivalent, Basic Fishing Kit (6 hooks and 100ft of line), Ruger 10/22 with Ammunition
Tools: 6-8" Fixed Blade, Sharpening Stone
Navigation: LED Headlamp with Spare Batteries; Compass & AO Map
As long as you're dressed "weather appropriate" in wool or synthetics (NO COTTON) with plenty of layers you'd be fine with a little skill and ingenuity.