This also all depends on how often you find yourself on the water and what types of trips you usually take. If you only take a river trip once or twice a year, you probably only need a few dry bags.
If you paddle year round, you’ll probably want a collection of bags: a 5-10L, a 30-40L, maybe a 60L, and a few heftier ones (100L+) for the big adventures.
If you aren’t sure which dry bag will work for you best (even after our recommendations!), consider getting two different types: a duffel or backpack dry bag and a rolltop bag. And if you know you need a specific size bag for a certain trip or to fit in, say, a rented raft or kayak, you may find yourself purchasing one or two to start.
Pro tip: If you are covering a lot of mileage and rivers, you’ll want at least three bags for gear of varying sizes. For short- to medium-length trips — whether it’s whitewater or flatwater — we recommend one bag for your shelter, sleep system, and clothes; one bag for your food and stove; and one bag for day access: things like snacks, maps, and emergency items.
For us, these bags tend to be three different sizes. (And if you plan ahead like us, you can even color-code them!)