Duck's Back Rain Cover
Which is why you can buy (drum roll) pack covers! These handy gadgets cost only a few bucks and are made of seam-taped, polyurethane-coated material so that they're all but 100-percent waterproof, allowing for the little moisture that can creep in around the harness, or when you're taking the cover off for access. They work great, although stuff in your pack isn't as accessible and the cover usually has to come off and then go back on when you want to fish out lunch or a fleece jacket. A good example of a pack cover is the REI Duck's Back Rain Cover, aptly named and reasonably priced at $22 (www.rei.com).
Over the years a few stabs at waterproof packs have been made, but the challenge of stitching up a seam-taped packitself a complicated item with great demands made on it for ruggedness and durabilityhas made such efforts few and far between. Today, however, progress in fabric and fabrication technology (ultrasound-welded seams, for instance) make waterproof packs more practical. As I've written about before, in the past six months Arc'teryx has introduced an innovative line of packs that don't have a stitch in them; they're seam-welded together with waterproof material. And, they have a serious suspension, plus features such as hydration bladder pockets, access pockets, and more. The cost still is pretty high: $429 for the mid-sized Naos 55 (www.arcteryx.com), for instance, though that's not yet in custom-pack terrain. For a person who really needs the waterproof feature it probably is within reason.
For more expert reviews of backpacks big, small, and bombproof, check out Outside Online's Backpacks Buying Guide.