Three different emergencies need three different bags, and most people prepare the wrong one. Build all three here, weigh them against what you can actually carry, and print a checklist. The point is not a perfect kit — it is a kit that exists, is packed, and is by the door.
The grab bag is for leaving in minutes: a fire, a gas leak, a flood warning, a knock at the door. It should be small enough that you grab it without thinking, and it should contain the things you cannot replace and cannot do without — medication, documents, keys, cash, a phone and a charger. Most evacuations in the UK are this kind, and most people have none.
The 72-hour bag is for being away from home for a few days with nothing: water, food that needs no cooking, warmth, a torch, a radio, first aid, hygiene. Seventy-two hours is the standard because it is roughly how long it takes emergency services to reach everyone in a widespread incident.
The stay-put kit is for the opposite situation: you cannot leave, or leaving is more dangerous than staying. A power cut in winter, a road closure, a severe weather warning. This is water and food for two weeks, warmth without electricity, and a way to charge a phone. It is by far the cheapest of the three to prepare because it stays at home and can be heavy.
Whatever you pack, put a copy of your documents in a sealed waterproof bag or a USB stick, keep some cash in small notes (card terminals fail in a power cut), and check the bag every six months. Medicines expire, batteries leak, children grow, and a bag nobody has opened is a bag of surprises.