A stuff sack is a simple fabric bag with a drawstring top. It organises your pack, compresses soft items like clothing, and keeps small things from scattering, but it does not keep water out. Rain running down your pack, a stream crossing gone wrong, or a leaky water bottle will soak straight through it. A dry bag, by contrast, is made from waterproof fabric with sealed seams and a roll-top closure that folds down several times and clips shut, creating a seal that keeps water out even when submerged briefly.

This difference decides everything about how you use them. Stuff sacks are for organisation; dry bags are for protection. Many beginners buy a full set of one or the other and end up either carrying wet gear or hauling unnecessary waterproof weight. The smart approach is to use each where it actually helps, which usually means a mix of both.

Your sleeping bag is the top priority. A wet sleeping bag loses much of its insulation and can ruin a trip, especially in cold weather, so it deserves a proper dry bag or a waterproof pack liner. The same goes for spare clothing you plan to sleep in and any down insulation, which is particularly vulnerable to moisture. Electronics, first-aid supplies, and paper maps also belong in waterproof protection, though a small zip-lock bag often does that job more cheaply than a dedicated dry bag.

Food is a borderline case. Most packaged food survives a splash, but a soaked food bag becomes heavy and messy, and wet packaging can leak. A lightweight dry bag for food is worth it on wet trips or routes with river crossings. For everything else, like a cook pot, a stove, or a tent that is already wet from the morning dew, a stuff sack is perfectly fine.

Dry bags weigh more than stuff sacks of the same size, because waterproof fabric and roll-top closures are heavier than thin nylon and a drawstring. Carrying a dry bag for every item quickly adds up, so be selective. One common ultralight strategy is to use a single large pack liner, essentially a big dry bag that lines the inside of your backpack, and to organise everything inside it with ordinary stuff sacks. This protects all your gear at once with only one waterproof layer.

Another approach is to use a few small dry bags for critical items and stuff sacks for the rest. Either way, test your system before a trip: put tissue paper inside a bag, close it as you would on the trail, and hold it under a tap or dunk it in a basin. If the tissue stays dry, your closure technique works. Many so-called waterproof failures are really just roll-tops that were not folded enough times.

Stuff sacks are lighter, cheaper, and easier to open and close repeatedly, which matters for items you reach for often, like snacks, a rain jacket, or a water filter. Compression stuff sacks can also shrink a bulky sleeping bag or jacket, though be careful not to store down gear compressed for long periods between trips, as that damages its loft over time.

Colour-coded stuff sacks are a simple organisation win. Assign one colour to clothing, another to food, and another to toiletries, and you can find anything in a dark tent without emptying your whole pack. Mesh stuff sacks are useful for items that need to dry, like a wet tent fly or damp socks, since they let air circulate instead of trapping moisture.

Start with a pack liner or a dry bag for your sleeping bag, add small waterproof protection for electronics and essentials, and use lightweight stuff sacks for everything else. Skip the pack rain cover as your only defence, since rain often finds its way in around the back panel and shoulder straps. With this mixed system, you stay dry in a downpour, keep your pack light, and still know exactly where everything is when you need it in the dark.