Zippers break. Cordage breaks. Which one can be fixed in the field? Keeping gear dry is as much forthought as technology. My rucksak is a robust, but simple German army unit with drawcord and flap. I further secure the contents, both for protection and organization in zip bags. If it rains hard I cover the sack with my poncho and head for cover. If you are carefull, there are many surplus units worth looking at. They must be listed as NEW or EXCELLENT condition. Avoid anything less and expect leather components to be junk. Some have very heavy and uncomforatble frames.