MJD wrote:No way to list only three items.
Totally agree.
Essential 1: You must stay warm. Hypothermia is your number one enemy. So you need dry shelter, dry bedding (sleeping bag and mat), water proof/wind proof outer layer, and two sets of clothes (one which you keep dry for when you aren't walking). Also take hat, gloves, boots, gaiters and socks to suit the conditions you will encounter. The shelter, sleeping bag and mat, and outer layer should all be chosen to suit the worst conditions (not the average) you might encounter where you are walking.
Essential 2: You must drink and eat. Your body can't stay warm and exercise for long periods without fuel, and you won't stay as alert as you need to be without food and water. Take light weight, high energy food (high calorie food). If we are talking absolutely essential, you don't need a stove if you take the right food - you can live on food bars for a week. Obviously a stove and good food is better for you and will make the trip more enjoyable.
Essential 3: You must know where you are and where you are going. Navigation aids are essential for safety and survival. A compass and maps minimum. GPS and backup batteries if you prefer. You'd probably survive without a torch or headlight, but a light is very nice to have.
Essential 4: Personal Hygiene & Medications. The minimum is a toilet spade, TP and hand-wash. Carry what ever else you need for your personal ablutions and daily medications. With more and more people using the bush it is essential that all walkers practice minimal impact walking.
Essential 5: You must be able to care for your injuries and make running repairs to damaged gear. A simple cut on your hand can become septic and poisonous in 24 hours without treatment. Sprains and strains, bites and general aches and pains all mean you should carry a basic first aid kit. Include a whistle, pocket knife, water proof matches, bushman insect repellent, spare laces (double as string), a few safety pins, strapping tape, 2 X Gauze bandage, Compression bandage, panadol/aspro, bandaids, sterile swipes, metho/disinfectant, thermal blanket and splinter kit. And maybe duct-tape.
And that's just the short list.
Obviously you can reduce the load if you are only on a day trip. I take waterproof trousers, poncho, boots, gaiters, hat, food-bars, water, navigation aids, TP, toilet spade and a slightly smaller first aid kit, plus my camera/electronic gear on all day walks.