Sea to Summit Flow 35L DryPack
Here's what other sites are saying:
If weekend backpacking's your thing, please allow Sea to Summit to humbly present the Flow 35L DryPack. It carries like a champ, thanks to an ergonomic back panel, ventilated shoulder straps, and a padded waist belt, but has one advantage that most packs don't: it's fully waterproof. The 420D nylon is laminated with TPU, fully seam sealed, and has a rolltop closure, so it keeps your gear dry whether you're caught in a spring rainstorm, skiing in soggy snow, or paddling a sunny river--the only water that'll get in will be your hydration bladder. It also has side compression straps for carrying skis (or anything else you think up), stretch mesh water bottle pockets, and a top haul loop, just in case.
The Flow 35L DryPack from Sea to Summit has a fully contoured, mesh/perforated foam waist belt to more comfortably carry heavy loads. It features several hypalon loops for attaching gear and side compression straps. It has deep stretch mesh side pockets and a 2-Liter volume outside zippered pocket.