Daypacks can certainly be waterproof. If you need a bag that’s completely waterproof, it’s best to search for a water bag with straps designed for hiking. However, it’s important to note that even those bags often have a roll-top closure and cannot be submerged for a length of time, but they will keep your items exceptionally dry in most situations. Packs made out of waxed canvas can often be treated to a waterproof rating as well with a spray or seam sealer. At the very least, it’s a good idea to purchase a bag that comes with a rain cover or to buy a rain cover that fits your bag for those times when Mother Nature decides to change up the conditions on your hike.