What belongs in an ultralight first aid kit is a question with a surprisingly light answer: for most solo three-season trips, a well-chosen kit weighs just 3 to 6 ounces and fits in a small zip bag, yet covers the injuries hikers actually get. Those injuries are overwhelmingly blisters, small cuts and scrapes, sprains, headaches, sunburn, and stomach trouble — not the dramatic emergencies that tempt people to pack a full pharmacy. The best kit is not the biggest one; it is the one you know how to use, can reach quickly, and actually carry on every trip instead of leaving behind because it is too heavy.

Start with blister care, because blisters end more hikes than any other minor injury. Carry moleskin or dedicated blister patches, a few adhesive bandages in different sizes, and a small piece of athletic tape that can also serve as a repair tape. Treat a hot spot the moment you feel it, not at camp when it has already become a blister: stop, clean the area, apply moleskin with a hole cut for the blister, and tape over it. Change socks if they are damp, and learn to recognise the difference between a friction blister and a pressure point caused by a boot or shoe that needs lacing adjustment, because tape alone will not fix a fit problem.

For cuts, scrapes, and wound care, keep it simple and clean. A few sterile gauze pads, a small roll of medical tape, butterfly closures for shallow cuts, and antiseptic wipes will handle most trail wounds, and a pair of nitrile gloves protects both you and anyone you help. Clean a wound with clean drinking water, apply pressure to stop bleeding, close it if it is shallow and clean, and cover it to keep dirt out. Carry a needle and thread or a safety pin not for stitching wounds — leave that to medical professionals — but for draining a blister safely or repairing gear, which is a far more realistic trail use.

Medications should be personal, minimal, and clearly labelled, because taking the wrong tablet in the dark helps no one. A few ibuprofen or paracetamol tablets for pain and inflammation, antihistamines for allergic reactions or itchy bites, and anti-diarrhoea tablets for stomach trouble cover most needs, plus any personal prescription medication you require, carried in its original packaging or a clearly labelled container. Add sunscreen and lip balm to prevent sunburn rather than treating it, and insect repellent if your area demands it — prevention weighs less than treatment and works better. Check expiry dates before each season and replace anything damp or damaged.

What can you leave behind? Most pre-made kits include items ultralight hikers never use: large trauma dressings for solo day hikes, multiple splints, bulky scissors, instant cold packs, and dozens of bandages in sizes you will never need. Leave the full-size scissors at home and carry a tiny pair or use your knife carefully; leave the SAM splint unless you are leading a group in remote terrain, and improvise a splint from a sleeping pad and trekking poles if you truly need one. Similarly, a whistle, a small emergency blanket, and a fire starter belong in your safety kit, not counted as first-aid weight, but they complement it and weigh almost nothing.

Finally, the most important part of any first aid kit is not in the bag at all — it is your knowledge. Take a basic wilderness first aid course if you hike regularly, learn how to recognise dehydration, hypothermia, and heat exhaustion, and know when to stop and seek help rather than push on. Tell someone your route and return time, carry a charged phone with offline maps, and consider a satellite messenger for remote trips where phone signal is unreliable. Pack your kit where you can reach it without unpacking your whole bag, practise opening it with cold hands, and replace anything you use the moment you get home, so the next trip starts with a complete kit, not a half-empty bag of good intentions.