Able to stuff down to a size so it fits into a pack's side pocket, the Hilleberg Akto offers more space than a bivi bag, and has a porch to store all your gear.

MSR Pocket Rocket proves less is more. Weight is just 3oz.

Essentially a huge drysac, the Sea to Summit Pack liner is probably the best way to ensure that the gear inside your rucksack stays dry when outdoors in the rain or when performing river crossings.