Why one big bag is a bad idea

Most paddlers start out with a single holdall stuffed with everything and jammed behind the seat. It works beautifully on a calm canal. Then you hit a gust on a windy stretch, the boat tips, you swim, and suddenly your spare fleece, your sandwiches and your phone are all marinating in the same soupy puddle of river water at the bottom of the hull. A dry bag only keeps things dry if it is sealed properly and if whatever is inside it is not going to puncture it from within.

Splitting your kit into several smaller bags does three useful things. It limits the damage if one bag leaks or gets left on the bank. It lets you find your first aid kit without emptying half the boat. And it makes the weight easy to distribute so the boat sits level rather than dragging its stern like a dog with a bone.

As a rough rule, aim for four bags: spare clothing, electronics, food and drink, and safety and first aid. If you are out for a full day on moving water, add a fifth for a shelter or group kit.

Sorting your kit into separate bags

Think about what absolutely must stay dry, what merely prefers to stay dry, and what can get wet without ruining your day. That order of priority decides which bag each item goes into.

• Clothing bag: a full spare set — thermal base layer, fleece, spare socks, hat, and gloves — in one bag. Pack it as a complete change so you never have to rummage. A dry bag of 10 to 15 litres handles this comfortably for a day trip.
• Electronics bag: phone, keys, car fob, power bank and any camera. Use a small 2 to 5 litre bag, and put the phone in a second sealed pouch inside it. Two layers sounds fussy until the day you need it.
• Food bag: snacks, flask or bottle, and a brew kit. Keep this separate so a leaking flask does not soak your spare socks.
• Safety and first aid bag: plasters, blister kit, tape, painkillers, a foil blanket, head torch, and any personal medication. This one should be the easiest bag to reach, not the one buried under everything else.

Label the bags with a strip of tape and a marker if you paddle with others. It saves an enormous amount of shouting on a chilly bank.

Sealing a dry bag so it actually stays dry

Roll-top bags fail for one of two reasons: too much air left inside, or too few rolls. Both are easy to fix.

Pack soft items loosely rather than cramming them tight. Leave a hand's width of empty fabric at the top, squeeze out most of the air — but not all of it, because a completely flat bag is hard to roll and the fabric creases at the corners. Then fold the top over firmly at least three times, pressing the air out as you go, and clip the buckle. Four rolls is better than three on a big bag.

Check the closure before it goes in the boat. If the two halves of the buckle will not meet without force, the bag is overfilled. Take something out rather than fighting it.

Old bags with a nick or a gritty fold will eventually let water in. Test them in the bath at home before a trip: fill with a rolled towel, seal, submerge for a minute, and see whether the towel stays dry.

Securing bags so they stay put if you capsize

A dry bag floating free in a swamped boat is a hazard, and one that drifts off downstream is a loss. Loose kit also shifts your weight and makes an already wobbly moment worse.

In an open canoe, tuck bags low and centred, and lash them to the thwart or a dedicated lashing point with a short length of cord and a quick-release knot. In a kayak, push bags forward and aft of your seat, and use the deck lines or a small length of shock cord to hold them against the hull. Keep the heaviest bag near the middle of the boat.

Never tie anything to yourself, and never use a knot you cannot undo with cold, wet hands. A simple loop passed over a cleat or a quick-release buckle beats anything clever.

Attach a short grab loop or a length of brightly coloured cord to each bag. If the worst happens, you can spot it in the water and haul it back in one movement.

When you do go for a swim

Stay with the boat if it is safe to do so, and let the bags do their job. Once you are back on the bank or back in the boat, open the bags one at a time and check for water inside. If a bag has leaked, dry the contents in the sun or swap into your spare clothing straight away — cold and wet turns from uncomfortable to serious much faster than most people expect.

After the trip, empty every bag, wipe them out, and leave them open to dry somewhere airy. Store them unsealed and loosely rolled. A dry bag looked after will last you a decade of river days; one left sealed and damp in a shed will smell like a pond by next spring.