A flask of tea is not just a drink on a coastal walk. It is a small, warm ritual that makes the difference between a brisk stroll and a proper day out. When the wind is cutting across the headland and the sea is the colour of slate, there is nothing better than unscrewing the cup, pouring a steaming cuppa, and feeling the heat travel right down to your boots. Get it right, and a humble brew becomes the best part of the day.

Why a flask of tea belongs on a coastal walk

Coastal paths are bracing by nature. Even on a bright day, the wind off the sea can drop the temperature by several degrees, and the salt air seems to sharpen your appetite. A flask of tea is comforting, portable and far more welcome than a cold drink when you stop on a clifftop bench. It also gives you a reason to pause, rather than marching past the best views. If you are walking with family or friends, one good flask can serve two or three people in enamel mugs, which feels generous without weighing you down.

Brewing a flask that tastes like a proper cuppa

A decent vacuum flask is the only piece of kit that really matters. Look for a stainless steel model with a wide mouth, a reliable seal and a cup that is big enough to drink from properly. Before you leave the house, preheat the flask: fill it with boiling water, screw on the lid, and leave it for two or three minutes. Empty it, then fill with your tea. This simple step can add an hour or more to how long the tea stays hot.

Tea that has stewed for three hours can taste bitter and metallic. The trick is to brew strong, but not harsh, and to remove the leaves or bags before they overdo it. For a one-litre flask, use three or four tea bags, or three heaped teaspoons of loose tea. Brew in a teapot or a large jug with freshly boiled water, give it four to five minutes, then strain it into the preheated flask. If you are brewing directly in the flask, use tea bags with strings so you can fish them out easily, and don't squeeze them — squeezing releases tannins that turn the brew bitter.

Milk is the tricky part. Adding milk to a flask can make the tea taste stewed and, over several hours, it may curdle. The better approach is to take milk separately in a tiny screw-top bottle, or use a splash of evaporated milk, which travels well. If you take sugar, add it to the flask while the tea is hot so it dissolves. A slice of lemon is a fine alternative, especially with a lighter tea.

Keeping it hot when the wind is against you

Even the best flask loses heat if you treat it badly. Fill it right to the neck to leave as little air inside as possible, then seal it immediately. Wrap the flask in a tea towel, a fleece or even a woolly hat before it goes in your rucksack. The middle of the bag is warmer than an outside pocket. On the walk, resist the urge to open the flask "just to check" — every time you unscrew the lid, you let out a rush of heat. Wait until you are ready to sit down and drink. If you are using enamel mugs, warm them first with a little hot tea, then pour the rest. And be careful: hot tea in a moving rucksack can slosh and burn, so always pour on a flat, stable surface away from the edge.

Snacks that earn their place in the rucksack

Tea is only half the picnic. Coastal walking calls for snacks that are sturdy, salty and satisfying. Crisps are the obvious choice, but a standard bag will crush into dust in a rucksack. Pack them in a hard plastic tub or a clip-top box, or choose thicker-cut crisps that can take a bit of knocking about. Salt and vinegar is the classic coastal flavour — sharp, salty and excellent with tea — while cheese and onion or prawn cocktail feel like a proper seaside treat. Bring a spare bag clip in case you cannot finish them.

• Crisps: pack in a rigid tub; salt and vinegar, cheese and onion, or ready salted.
• Pork pie or sausage roll: wrapped in foil, they survive a rucksack and taste great cold.
• Cornish pasty: a full meal in pastry, best eaten with a view of the sea.
• Oatcakes and cheese: sturdy, savoury and made for a flask of strong tea.
• Flapjack or fruit cake: slow-release energy for the climb back up the cliff.
• Nuts and dried fruit: light, tidy and easy to nibble while walking.

A coastal picnic worth the climb

Find a sheltered spot — behind a wall, in the lee of a gorse bush, or on a bench facing away from the wind. Pour the tea first, then open the snacks. Let the steam warm your face before you take the first sip. If the tea has gone lukewarm, don't despair: it still beats a cold bottle of water, and the crisps will taste just as good. Pack out every wrapper, crust and apple core, and leave the clifftop as you found it. Then screw the lid back on, tuck the flask into the middle of your rucksack, and set off again with a warm middle and a happy heart.