For kayakers, rafters, coasteerers and anyone else who spends a lot of time in a wet environment this Sea to Summit Ultrasil Waterproof daypack is well worth checking out.
Made from superlight fabrics it weighs just 90g and has a siliconised outer layer with waterproof roll top and double stitched, fully taped seams to keep your kit bone dry. There’s also an external bungee cord for carrying additional kit on the outside of the pack.
To be fair you wouldn’t use it for a carrying heavy loads or on a full day hike since to keep the weight down the design is very minimalist, with lightweight shoulder straps and no back padding or hip belt, but if you’re doing short portages or carrying gear around that simply must stay dry such as a sleeping bag or electronic stuff then it does a great job.
And it’s so small and light that you can also carry it in your main pack as a spare daypack, or to keep stuff dry within said pack.
You also get a tiny stuff sac but it’s a bit of a mission to get the back into it and I can see most people either ditching this or using it for some other storage purpose.