Since not all of your outdoor gear can be waterproof, you may want a waterproof backpack. For short river hikes you can get a completely waterproof backpack to carry your food and drink, a phone, and a change of dry clothes. They are easy to swim with, just float behind you and add some buoyancy. In tricky situations wear your bag in front as a float.
Seen on Aliexpress:
Canoeing and swimming bag US$7 to $20 subject to size.
Sealed backpacks keep your kit dry. Choose the robust ones used for canoeing. They can cope with frequent immersion and provide extra buoyancy.
The size of your backpack depends on the length of your trip.
A small day pack with snacks, a change of clothes and a bin liner is all you need for a day in the rain or water.
For overnight trips you may want to carefully plan your kit.
Keep you bag content minimal.
If you only venture out for a day, a waterproof day pack might be useful. In it you keep your food and a change of clothes for after your excursion. Protect your stuff from water, sand and dust during river trekking, drifting, swimming and beach leisure. A small waterproof bag inside keeps your wallet and car keys dry.
If you keep a change of clothes waiting for you in your car, then the clothes in your day pack let you dry out for a lunch break, while your wet clothes can drip dry a bit.
After your lunch break, you pack away the wet kit as it's not nice to put on clammy clothes.
Instead you wear your dry clothes for the way back, ready to get wet,
since you have a dry set in your car.
A few manufacturers offer waterproof submersible bags that you can carry into the water. They can be completely sealed and stay dry when you go into the water. A good backpack has a hip belt that distributes the weight further down to reduce shoulder load.
Some backpacks, like the Rain Shadow Outdry, claim to be completely waterproof, so you can use them for river hiking. Waterproof and floating, they keep your items inside dry, while keeping dirt or sand out.
Phuket is a wonderful island if you stay away from the tourist traps. Up in the mist rain forest life is beautiful. Mountain trails cross rivers and wind along small lakes. The lush foliage is covered in morning dew or rain drops and smells lovely. It's a warm wet paradise.
It rains a lot in our area, mostly in the morning when I go out with another park ranger. Our clothes are very breathable, but not waterproof and get completely soaked in the rain, but the backpack contents always stay dry.
From early morning to afternoon we patrol the rain forest. While walking the trails, crossing rivers and lakes, we often have to go into the water fully clothed. Wet clothes dry quickly, but wet food or a wet equipment can cause problems. Waterproof backpacks keep our gear dry and working. They are essential for our work.
When the sun comes out we enjoy a snack break while our clothes quickly dry.
Most afternoons on our way back a heavy downpour hits us for one or two hours.
It's quite refreshing to get soaked again.
Back at our base we take a shower in our clothes to rinse and clean them up.