There is a particular kind of misery that comes from opening a rucksack at 700 metres in February and finding a frozen sandwich, a rock-hard flapjack and a flask of lukewarm tea. It is entirely avoidable. With a bit of thought at the kitchen table, a cold hill day becomes something to look forward to — a proper sit-down meal with a view, eaten while the wind nips at your ears and steam curls off the top of a cup.

Why cold weather changes what you should pack

Two things happen when the temperature drops. Your body burns through fuel faster as it works to stay warm, and your food behaves differently in the pack. Bread goes stiff and unpleasant. Chocolate turns chalky and pale. Anything wet and sloppy in a plastic bag tends to leak into everything else.

Fat is your friend here. A cheese sandwich with plenty of butter holds together and satisfies in a way a lean one never does. Oily, dense, savoury food travels well and eats well when your hands are cold and your appetite is a bit odd. Warm drinks are worth more than the calories they carry — they lift the spirits as much as the body temperature.

Getting the best from your flask

The single best upgrade to any winter walk is treating your flask with a bit of respect. Most people fill it half-heartedly and wonder why the contents are tepid by noon.

• Preheat it. Fill the flask with boiling water, screw the lid on, and leave it for five minutes while you finish packing. Tip that water away, then fill with what you actually want to drink.
• Fill it to the brim. Air is what steals heat. Leave no gap at the top.
• Screw the lid down promptly and don't open it just to check — every peek costs you degrees.
• Insulate the flask itself. A spare woolly hat or a fleece sleeve tucked around it makes a measurable difference.
• Take two smaller flasks rather than one giant one: one for soup, one for tea. That way you're not choosing between a hot lunch and a hot drink.

Soup that stands up to a rucksack

Thin, watery soup sloshes, cools quickly and spills. Thick soup is what you want — something you could almost eat with a spoon if the flask leaked. Red lentil and carrot, split pea with a little bacon, spiced butternut, potato and leek blitzed smooth: all of these hold their heat and feel like a proper meal. Blend them well at home so there are no lumps to negotiate with cold fingers.

Season boldly. Cold dulls flavour, so a soup that tastes perfectly judged in your warm kitchen will taste a bit flat at the top of a cairn. Add a good grind of black pepper, a pinch of chilli, a squeeze of lemon or a spoonful of cream cheese stirred through at the end. Pack oatcakes separately to dunk, and a small square of cheese to crumble in.

Oatcakes, cheese and other dependable rations

Oatcakes are close to perfect fell food: sturdy enough to survive being sat on, dry enough not to spoil, and a fine vehicle for anything fatty or salty. Build your lunch bag around things that improve rather than suffer in the cold.

• Oatcakes and hard cheese — mature Cheddar, or anything crumbly and strong.
• Cured sausage sliced at home, wrapped in greaseproof paper.
• A pork pie or a slice of good game pie, which travels beautifully in a rigid tub.
• Boiled eggs, peeled at home so you're not juggling shells in a gale.
• Malt loaf, fruit cake and flapjack — dense, sweet and unbothered by frost.
• Nuts, dates and dried apricots in a small bag you can reach without taking your pack off.
• Crisps in a rigid tub, if you want salt and crunch without the dust.

Bread does freeze, so if you're set on sandwiches, butter it generously first — the fat acts as a barrier — and keep them in an inside pocket rather than the top of the pack.

Sweet things, hot drinks and the second flask

Sweet food is a genuine morale tool on a cold day, and it's the easiest thing to get right. Chocolate should live in a chest pocket where your body heat keeps it soft. Mint cake, toffee and boiled sweets all work well. A handful of jelly babies at the top of a steep pull has revived more walkers than any energy bar ever will.

For drinks, strong tea with a slice of lemon keeps its edge. Coffee is fine if you like it stewed. Hot squash or spiced apple goes down well with children and anyone who doesn't want caffeine on a long descent. Add a little sugar to whatever you take — it's fuel, and it tastes better on a hill than it does at home.

Eating well on the hill: timing and comfort

Stop to eat before you are cold and hungry. Once you're shivering, you'll rush the meal, get colder still, and take an hour to warm back up. Pick a spot out of the wind, ideally facing the sun, and sit on your rucksack or a foam mat rather than bare rock.

Keep everything for lunch in one bag so you're not rummaging with your gloves off. Open the flask, pour, and get the lid back on quickly. Eat little and often rather than saving everything for one heroic stop — a few oatcakes and a cup of soup at a col, then cake on the summit, keeps you steady all day.

Pack it well, eat it warm, and a cold hill day turns into the sort of walk you'll be planning again before the weekend is out.