There is a quiet moment on every fell walk when you realise your pack is either helping you along or quietly ruining your day. You notice it about an hour in, usually on the first proper climb, when the straps dig in or the load shifts sideways with every stride. Get the pack right and you will barely think about it again until you swing it off at the summit. Get it wrong and you will feel every one of those miles in your shoulders and lower back.

Why the pack matters more than most kit

Boots get all the attention, and rightly so, but a backpack is the piece of kit that stays with you from the car park to the trig point and back. In Britain we walk in weather that changes its mind three times before lunch, so a day pack has to carry a surprising amount: waterproofs, a spare fleece, food, water, map and compass, and a small emergency kit that you hope never to use. That load has to sit comfortably against your back for five or six hours over rough ground.

The good news is that you do not need to spend a fortune. A well-chosen pack from a reputable outdoor brand, bought in the sale if you can, will happily last a decade of regular rambling. What matters far more than price is size and fit.

Why 20 to 30 litres suits most day walks

For the vast majority of British day walks, a pack of 20 to 30 litres is the sweet spot. It swallows everything you need for a full day out without tempting you to carry the kitchen sink. A 25-litre pack will typically hold:

• A lightweight waterproof jacket and over-trousers
• A fleece or insulated mid-layer
• Flask, sandwiches and a decent amount of snacks
• One to two litres of water
• Map, compass, headtorch and a small first aid kit
• Hat, gloves and a spare pair of socks

Go smaller, around 15 to 18 litres, and you have a fine summer evening pack for a low-level amble. Go bigger and you are into winter conditions, carrying kit for children, or long days on the Scottish hills where daylight is short and the weather can turn properly serious. A 35 to 40 litre pack is not wrong, but for most people most of the time it simply encourages overpacking.

Bear in mind that quoted volumes are measured with the lid closed and can vary between makers, so a 25-litre pack from one brand may feel roomier than another.

Fit is everything: straps, back length and hip belts

Weight should sit on your hips, not your shoulders. That single principle guides everything else. Look for a pack with a padded hip belt that wraps around the top of your hip bones, and shoulder straps that curve comfortably without pinching under the arms.

• Back length: check the pack suits your torso, not just your height. Many packs come in sizes or have an adjustable back panel.
• Shoulder straps: padded, with a sternum strap to stop them sliding outwards.
• Hip belt: wide enough to spread the load, with a good buckle and ideally a small pocket for a snack or phone.
• Load lifters: small straps at the top of the shoulders that pull the pack closer to your back on steep ground.

When you try a pack on, load it with something heavy, around 6 to 8 kilograms, then adjust in this order: loosen everything, fasten the hip belt first, tighten the shoulder straps, then the sternum strap, then the load lifters. If a shop will let you walk around with it for twenty minutes, take them up on it. If you are shopping online, buy from somewhere with a straightforward returns policy and test it indoors on carpet before you commit.

Features worth paying for

A simple pack is often a better pack. Too many straps, pockets and zips add weight and things to snag on hawthorn. That said, a few details genuinely earn their place:

• Ventilated back panel: you will still sweat on a Lake District climb, but a channel or mesh panel helps.
• Side compression straps: keep a part-empty pack stable.
• A lid or top pocket: perfect for keys, sun cream and a map you want quick access to.
• A rain cover or water-resistant fabric: British weather being what it is, this is close to essential.
• Durable fabric: look for a ripstop nylon or similar, with reinforced base panels.
• Sturdy zips and buckles: the parts that fail first on cheap packs.

Packing it well

How you pack matters almost as much as what you buy. Keep heavy items, water and food, close to your spine and at mid-back height so the load sits over your centre of gravity. Put soft, light things like a spare fleece around them. Keep waterproofs and your map near the top, or in an outside pocket, so you are not unpacking everything on a windswept col when the rain arrives.

That small emergency kit is worth the space every time: a basic first aid kit, a whistle, a headtorch, a foil survival bag and a spare energy bar. Add a paper map and compass even if you carry a phone, because batteries die in the cold and signal disappears in the valleys. Wrap anything that must stay dry in a dry bag or a simple plastic bag.

Looking after your pack

After a muddy day on the Pennine Way or a damp trudge through the Yorkshire Dales, empty your pack completely, shake out the crumbs, and sponge off any mud with lukewarm water. Never put it in a washing machine, as the detergent and agitation will destroy the water-repellent finish and the padding. Dry it somewhere airy, out of direct sun, with the lid open. Check the buckles and straps now and then, and tighten any that have worked loose.

With a bit of care, a good 25-litre pack will serve you faithfully for years, quietly doing its job while you get on with the far more important business of enjoying the view.