Start with your layers, not your kit list

British weather rarely respects the forecast. A morning that starts mild and still on the valley floor can turn into a cold, wet slog across an exposed ridge by early afternoon, and the reverse is just as true — you set off in a jacket and end up peeling it off within a mile of climbing. The answer is not a bigger rucksack. It is a layering system you can add to and strip back without stopping for long.

• Base layer: a short-sleeved or long-sleeved synthetic or merino top that wicks sweat away from your skin. Cotton is the one fabric to leave at home; once it is damp it stays damp and chills you quickly.
• Mid layer: a lightweight fleece or thin synthetic jacket. This is the layer you will take on and off most often, so choose something you can stuff into the top of your pack one-handed.
• Shell: a waterproof jacket with taped seams and a hood that stays up in wind. Breathable fabrics are worth the money, but a simple well-fitting shell beats an expensive one that flaps.
• Legs: walking trousers that dry fast. Add waterproof overtrousers if rain is likely or if you will be crossing wet ground and long grass.

Pack the layers you are not wearing at the top of your rucksack, not buried at the bottom. When the weather turns, you want to be reaching for your jacket in seconds, not unpacking your entire day.

What belongs in the rucksack itself

A 20 to 25 litre pack is plenty for a day out in the hills, and a 30 litre one gives you room for a flask and a bulkier layer in winter. Whatever the size, aim for a pack that sits close to your back with a decent hip belt, because a bag that swings about will tire you out long before the terrain does.

• Spare socks in a dry bag — wet feet cause blisters faster than distance does.
• Hat and gloves, even in July. Summits are colder than car parks.
• Sun hat and sunscreen for the days that surprise you.
• Blister plasters and a small roll of tape.
• A head torch with fresh batteries. It weighs almost nothing and it matters enormously if the day runs later than planned.

Water, food and keeping your energy up

You will drink more than you expect, particularly on a warm day with a long climb. Carry at least 1.5 litres for a moderate day out and closer to two litres in summer or on a route with no reliable water source. A flask of something hot is a genuine morale booster in cold, damp conditions, and it costs you very little in weight.

Food should be easy to eat while walking rather than something that needs a fork and a flat rock. Bring more than you think you need:

• Sandwiches or a filled roll for lunch
• Flapjack, oatcakes or malt loaf for slow-release energy
• Nuts, dried fruit or a handful of chocolate for a quick lift on a steep section
• Something salty — crisps or a handful of salted nuts — to replace what you sweat out

Eat little and often rather than saving everything for a summit lunch. The moment you feel a dip in energy on a long ascent, it is already a little late.

Navigation: paper first, phone second

Phones are wonderful until the battery dies or the signal vanishes, which in the British hills is often exactly when you need them. Carry a paper map of the area you are walking, in a clear case, plus a compass you actually know how to use. If you have not used one since school, a short refresher course or a practice session on a familiar local footpath is time well spent.

Tell someone at home where you are going, what route you intend to take and when you expect to be back. Add a whistle to your pack — six short blasts is the recognised distress signal — and a small power bank for your phone. Take a photograph of the route on the map before you set off; it is a useful backup and no weight at all.

Emergency shelter and the small things that save the day

An emergency shelter, sometimes called a bothy bag, is a lightweight fabric bag you sit inside to escape wind and rain. It folds down smaller than a paperback and can turn a miserable half hour into a manageable one, particularly if someone in the group is cold, tired or slightly injured. Add a foil blanket as well, and consider a basic first aid kit with plasters, painkillers, a bandage and any personal medication.

Other small items earn their place surprisingly often: a midge head net in the Highlands in summer, a small repair patch for a leaking mat or jacket, a penknife, and a bin bag to sit on or to keep your pack dry. None of it weighs much. All of it is welcome when the day does not go to plan.

Footwear and the final check

Boots or sturdy walking shoes with a decent tread and a bit of ankle support will handle mud, rock and wet grass far better than trainers. Break them in on shorter walks before committing to a long day, and pair them with socks that fit properly — a seam in the wrong place will find your heel within three miles.

Before you leave the house, run through a simple check: layers, water, food, map, compass, shelter, torch, whistle, phone. Then look at the forecast one more time and adjust. Pack for the day you might get, not just the one you are hoping for, and you will be comfortable, safe and free to enjoy everything the British countryside has to offer.