Helixot has made a backpack so extreme it can keep up with the most daring of cross-country trekkers.  The XO 6.2 Backpack ($110) is completely waterproof and totally submersible for wherever the trail might go.

And just in case some accident were to ever penetrate the special coated fabric, the Helixot XO 6.2 also has a watertight PVC compartment for holding electronics and other important items completely dry.  It has a rigid back built right in but is neoprene padded to make it a comfortable fit for taking your adventure far afield.  The ergonomic design helps streamline your hiking profile even if you are swimming or boating part of the way to your camp.