Water proofing
My experience is with backpacking so far. Bike touring will be this summer. In hauling weight on my back, I prefer the pack to be simple with few additional "features". Closure should be foolproof as well as light and simple, say roll top or drawstring. The only items that need to be dry are clothing and sleeping bag. These are kept dry in siliconized, waterproof stuff sacks which are available in sizes and shapes from about one liter to several gallons and weigh an ounce or two. The fabric is indeed waterproof and the seams sealed with silicon sealer available for tent seams. These actually hold air and you can blow them up like a balloon. Trash bags I've found, like others, to be delicate and don't last. What I have had good durability with is trash compactor bags which are much sturdier than plain trash bags. My most used backpack has had the same compactor bag for over a year. This pack has not had daily use for that period of time, such as in a trans-continental tour, but it has had many days of use.