Very few backpacks—except for a wet bag you might take on a river—are 100 percent waterproof because that would require a rubberized, roll-top closure, and extra seam sealing at the zippers, which adds unnecessary weight. There are, however, a lot of backpacks out there that, short of immersing them in a puddle, will keep your stuff plenty dry during a commuting downpour.
Patagonia's new 28-liter Atacama ($79; Patagonia.com) may be just what you need. Think of the interior pocket as your office, with its key lanyard, organizational dump pockets for pens, phones, and notebooks, and a raised, padded sleeve big enough for your 17-inch computer. That means the exterior pocket, separated from the interior by a waterproof barrier, is your gym bag, in which you can store wet swimsuits, sweaty running clothes, or anything gross and grimy you don't want to smear on your thesis. Add extras like a separate fleece-lined zipper pocket accessible from the top for your sunglasses, exterior compression straps for bulky items like jackets or skateboards, and a durable, water-repellent finish, and you can use this pack for the classroom, spring break adventures, or commuting to the grocery store.
Eagle Creek's new Cicada 28L ($150; eaglecreek.com) is yet another great option. Weather-resistant and travel savvy, the Cicada not only has the requisite bells and whistles like a padded computer/hydration sleeve big enough for a 17" laptop, a fleece-lined sunglass pocket, and a front zippered document pocket for traveling, but it also has an innovative "split wing" cover that secures with ratchet-lock buckles, providing extra protection from both inclement weather and unwanted pickpockets.