Good article by George Jasper explains it well:
The “Bugout Bag”
In “spook speak” a “Bug Out Bag” or “BOB” is the minimum essential kit needed for escaping an area where hostiles are searching for you, with intent that you would be captured, interrogated, tortured, or killed. It contains only essential items to sustain stealthy tactical movement out of danger. Usually, only food, navigation, communications and mission-critical protective gear are carried.
Water is something an “evader” is trained to find along the way. An escape and evasion or “E&E kit” contains an EMPTY water container, drinking tube, filter, and treatment chemicals, but no water “supply.” The season and operating environment determine what clothing and shelter is necessary to survive. E&E objectives are security, stealth and mobility, to avoid detection as you move out of danger to your extraction point. You aren’t just leaving an area, but going somewhere in particular in order to get home alive!
In the real nightmare scenario, the evader would scrounge from dead enemy or civilians. What do “they” have which will protect and sustain you? . Grab whatever it takes to nourish, hydrate, navigate, communicate, medicate, and keep moving on! Weapon, ammo, optics, food, first aid and medical, tools and sharps, cordage, communications or navigation aids, flashlight with green and IR filters, bug spray, gloves, socks, shoes, sunglasses, hat, etc.
Glass the terrain ahead prior to movement to avoid detection. Build a “hide” at night to shelter from the environment and to stay hidden. Small tools and cordage help, but the rule is to prioritize stealth and mobility, leave heavy, bulky, noisy items behind.
In “prepper speak” the BOB is a personal survival kit (PSK).
You control its size by selecting its container.
First Line (A Level) is your “Every Day Carry” or “EDC.” These are items you always have on you, all the time, which will likely be all that you have with you when your office building catches fire, the plane crashes, or you miss the last boat off Fantasy Island In Hell. One example is the “survival tin” you make to fit in an Altoids tin to carry in your pocket. A mini kit beats nothing, but provides false security, because if you REALLY need it, you will sure wish you had brought more with you.
No small group of items which fits in your pocket will overcome all adversities. The purpose of the tin is to provide basics which help you focus and improvise better gear to make your ordeal tolerable. Decide how much weight and bulk you can really carry. Then design your kit in Levels which build on and support each other:
Second Line (B Level) is a “small” belt pouch – “ideally under a kilo” about 2 pounds to supplement your EDC, keep in your desk, briefcase or vehicle. Mine is shown in the accompanying sidebar.
Third Line or (C Level) is the “Survival Ruck” or “72 hour pack” containing clothing, shelter, water, food, first aid kit and tools for several days, at least a 72 hour period.
Fourth Line (D Level) is the Deployment Bag which supplements all the above for resupply beyond immediate needs, for two weeks or more, from your aircraft, boat or motor vehicle.
Priorities address shelter first: clothing, raingear, boots, tent/tarp.
Water is next. Get a good water purifier and food grade storage containers. Water filters can crack or clog in below freezing weather. In winter, boil water or use chemical sterilization. In hot climates at minimum use filtration to remove turbidity followed by UV sterilization (SOLAS).
Food is of lower priority. Most people can survive with moderate discomfort for a week or so without food as long as they remain well hydrated. A small amount of emergency food is a morale booster, which gives a needed burst of energy for essential exertion or warmth.
Your PSK should plan for at least Level II and provide at least The Ten Essentials:
CATEGORY - EXAMPLES, SUGGESTIONS:
1. Shelter – Hat, contractor garbage bag or poncho, 550# cord, fleece vest, extra socks, VS17
2. Fire – BIC lighter, Sparklite Kit, waterproofed matches, Esbit stove and fuel
3 Light – LED light on zipper pull, plus Petzl headlamp
4. Hydration – Water Storage and purification – canteens & cup, Sawyer Mini filter, Micro-pur tablets, Steri-pen. Foodgrade containers
5. Communications - Signal mirror, whistle, cell phone, VS17, rescue strobe, VHF airband/marine transceiver
6. Navigation - Map and orienteering compass on dummy cord essential backup to GPS
7. Nutrition - Emergency food, peanut butter + Mainstay 2400, Military Speedhook fishing kit.
8. Tools & Sharps - Fixed blade knife, multi-tool, trowel, folding saw, machete or hatchet
9. Health & Medical - First aid kit, and necessary personal meds for 72 hours.
10. Personal items - Extra eyeglasses, sunglasses, ID card, keys, etc.)
If you aren’t in shape, carrying more than about 10 kilos for ten “clicks,” may exceed your limits of physical stamina. Go out there and test your equipment at least twice a year, even if it is just camping in the backyard during a rain or snowstorm. How else will you ever know?
Decide what environmental conditions your BOB is intended to see you through. Then test, evaluate and adjust your gear accordingly, but realistically. For civilian all-hazards contingency planning 3 to 5 days this is a good planning standard to manage evacuation until you can reach a safe area. Tailor your kit for the most likely scenarios: hurricane, wildfire, winter storm, flood, etc. Plan for “All Hazards” to provide shelter from expected weather, clean/safe drinking water, food, first aid, navigation, communications, security, fire, sanitation, and any unique medical or family needs which you have. Will it all fit in your bag? Then weigh it. Can you carry it?
Experiment. Live out of it for a weekend and see what works and doesn’t. Take notes and make improvements. Evaluate your route and plan where you might cache food, water, etc. to resupply when what you carry runs out. A rubber wheeled, steel frame folding luggage cart works well on level surfaces. Off road jogging strollers are good too.
Think outside the box.
